I. Introduction
The relationship between municipal and international law within the UK constitutional order is typically regarded as governed by the dualist principle. A separation is said to exist between laws of international and domestic origin; these two bodies of laws – as the UK Supreme Court noted in R. (SC) v Secretary of State for Work and Pensions – “operate in independent spheres”.Footnote 1 This separation is a product of, and serves to uphold, the domestic allocation of constitutional authority between Parliament, executive and courts.Footnote 2 Parliament’s role as primary legislator is, so the argument goes, protected from interference by the executive in the discharge of its foreign affairs prerogatives by a requirement that international treaty obligations are effective in domestic law only when incorporated by legislation.Footnote 3 Dualism, it is argued, secures a stable relationship between domestic and international legal orders that respects the municipal division of governmental power.Footnote 4
Endorsements of the dualist principle are commonplace. The UK Government uses the language of dualism to justify policy.Footnote 5 Legislators rely on dualism in describing the UK’s constitutional arrangements,Footnote 6 to explain the autonomy of domestic law from international legal obligations,Footnote 7 and for its (supposed) methodological stipulation that treaty obligations have domestic legal effect only when incorporated into domestic law by legislation.Footnote 8 Judicial decisions suggest a clear division between domestic and international legal orders,Footnote 9 specifically in relation to treaties to which Parliament has, and has not, chosen to give domestic effect.Footnote 10 The dualist principle, it seems, remains strongly influential as a description of and normative guide to UK constitutional law.
Our argument is that the principle has, in fact, ceased to operate effectively as either. First, we contend that, as a doctrinal guide dualism provides only a partial account of the relationships between international law and domestic laws which focuses on the direct effects – or absence of such effects – of treaty obligations. The very concept of dualism directs attention towards oppositional alternatives; according to dualist orthodoxy, norms of international origin are in the domestic context either incorporated or they are not; they either have domestic legal effect or they do not.Footnote 11 Dualism therefore has something of a reductive character, leaving (or failing to account for) significant grey spaces between the various divisions – internal/external; justiciable/non-justiciable; effective/non-effective – which it seeks to preserve. The simplistic nature of the principle, we suggest, fails to capture more complex yet commonplace interactions between the domestic and international legal orders.
Second, we argue that dualism’s emphasis on a qualitative distinction between laws of domestic and international origin fails to account adequately for the significant body of hybrid norms in the UK constitution – that is, norms (predominantly in the spheres impacted by EU and European Convention on Human Rights influences) that are better understood as cogenerated products of the interaction between domestic and international legal orders. Dualism therefore reflects a dichotomy which, as a matter of constitutional practice, has been undermined by decades of proximity between the domestic and international legal orders.
Third, dualism focuses on the event or moment – incorporation, for example – which determines whether an international legal norm is or is not domesticated. This “event” focus distracts from the processual nature of the interaction between domestic and international legal orders. Dualism ignores dynamic, evolutionary developments and pressures that complicate and destabilise the supposedly linear relationship between international and domestic laws. We argue that the domestication of an international legal norm should be seen as a long-term and potentially fluctuating process.
In summary, this article reconsiders dualism’s viability as the explanatory constitutional principle on the relationship between UK domestic and international legal orders. We argue that dualism depicts a relatively simple, coherent and stable nexus between the domestic and international legal orders and that this is at odds with a relationship that is, on our analysis, best seen as complex, fragmented and dynamic.
In the opening substantive section (“The ‘Dualist’ Constitution”) we offer an orthodox, dualist account of the UK constitution. In the next section (“A Fragmented Relationship”) we address the fragmented nature of the relationship between the UK domestic and international legal orders, dividing our analysis into three subsections. We contend, first, that dualism’s basis in oppositional alternatives – incorporated/unincorporated, for example – creates a partial, incomplete picture of the relationship that fails to recognise the complexity of the interaction between the domestic and the international; second, that the dualist notion that a norm or legal instrument is either domestic or international fails to account for hybrid norms, cogenerated through the interaction between domestic and international legal processes; and third, that dualism treats domestication as an event when, on our analysis, it is a process.
In the third and final section, we examine connections between the fragmented and complex relationship between the UK domestic and international legal orders and the recent UK political environment. We consider alternative means of conceptualising the relationship between the UK domestic and international legal orders and conclude that its complexity defies neat categorisation.
Throughout this article and in each aspect of our analysis we contend that, contrary to dualism’s emphasis on simplicity, coherence and stability, there is a fragmented relationship between UK domestic law and international law: a relationship involving multiple moving parts that do not fit together as a coherent or neatly expressable whole. For some audiences coherence, simplicity and neatness are the hallmarks of legal analysis: perhaps for those audiences a dualist analysis is instinctively attractive. We suggest, however, that our interrogation of the relationship in this article reveals deep flaws in a dualist analysis and that a simple or neat concept that would take dualism’s place is not available. The end point of our examination is not, then, an alternative lens or concept that makes everything simple, neat and clear, but a picture of a complex, fragmented and dynamic relationship that can only be seen as such.
II. The “Dualist” Constitution
Regulation of the interplay between internal (domestic) and external (international) norms is a core function of state constitutions, with national constitutional laws setting the primary rules that govern their intersection.Footnote 12 The concepts of monism, which regards international laws and domestic laws as one body of norms, and dualism, which treats international law and domestic law as operating in “independent spheres”,Footnote 13 are at opposite ends of a spectrum of approaches governing the relationship between internally- and externally-generated rules.Footnote 14 The UK constitution has traditionally been viewed as tending towards the “dualist” end of this spectrum.Footnote 15
Dualism provides an indicator of constitutional identity,Footnote 16 and sets the methodology for introducing international legal norms into the domestic legal order.Footnote 17 Recognised as a necessary derivative of the concept of parliamentary sovereignty,Footnote 18 the idea of dualism suggests that “a state’s domestic legal order is separate from the international legal order because the two are distinct in form, purpose and sphere of validity”.Footnote 19 Interaction between these spheres is formally contingent, it is argued, on domestic incorporation. On the orthodox account, a particular treaty entered into by the UK Government can become part of the UK legal order only by Parliament legislating to give it effect in domestic law. David Feldman argues that dualism provides a “filter” that regulates the extent to which external legal norms infiltrate the jurisdiction. This “filter” provides insulation to the domestic constitution and, in turn, to its institutions:
there are sound reasons for having filters at national level to control the way in which the obligations affect national law- and policy-making. The principled reason is the desire to uphold constitutional guarantees, including the rule of law, and keep in the hands of the nations the democratic control of and accountability for national law and policy, in order to maintain the legitimacy of politics and public law in the state. The pragmatic reason is that international obligations may be contrary to the national interest and may derail important national objectives.Footnote 20
Recognition that dualism is a “necessary corollary” of parliamentary sovereignty has clear implications for the domestic separation of powers.Footnote 21 The executive’s prerogative power to “make and unmake treaties” is consistent with “the rule that ministers cannot alter UK domestic law”Footnote 22 on the basis that while treaties bind the UK internationally, without incorporating legislation they will not “give rise to … legal rights or obligations in domestic law”.Footnote 23 From this perspective dualism “exists to protect Parliament”,Footnote 24 guarding against the extra-legislative expansion of executive power.Footnote 25
Dualism similarly limits the judiciary’s capacity to introduce rights and obligations into domestic law without incorporating legislation.Footnote 26 The “constitutional orthodoxy” on this point has been outlined by Lord Kerr:
Two dominant principles have traditionally restricted the use of international treaties in British domestic law. The first is that domestic courts have no jurisdiction to construe or apply treaties which have not been incorporated into national law; that they are effectively non-justiciable. The second is that such treaties, unless incorporated into domestic law, are not a part of that law and therefore cannot be given direct effect to create rights and obligations under national or municipal law.Footnote 27
Dualism, so the argument goes, protects the domestic constitutional order by safeguarding Parliament’s legislative autonomy from interference by the executive in its conduct of foreign affairs under the royal prerogative and by limiting judicial efforts to domesticate norms in “unincorporated” treaties. In short, “[i]f treaties have no effect in domestic law, Parliament’s legislative supremacy within its own polity is secure”.Footnote 28
III. A Fragmented Relationship
Whilst the examples above suggest that the dualist view of a relatively simple, coherent and stable relationship is resilient, a half-century long period of integration between the UK and European legal orders has placed “the binary logic of strict dualism” under considerable pressure.Footnote 29
The UK constitutional landscape – particularly in its accommodation of the supremacy of EU law, its ECHR-informed approach to rights protection and, more generally, the growing prominence of international legal influences in the domestic legal orderFootnote 30 – underwent significant change in this period.Footnote 31 The latter half of the twentieth century also saw a broader reconfiguration of international law, with the state-centric core of international obligations increasingly accompanied by international agreements conferring rights on individuals.Footnote 32 The UK’s acceptance, since 1966, of the right of individual petition to the European Court of Human Rights demonstrates the potential for an international agreement to influence the domestic legal order even in the absence of incorporating legislation.Footnote 33
In 2008, Sales and Clement recognised this growing tension, opening an assessment of “the developing framework” surrounding the treatment of international law in domestic courts with the suggestion that “[i]ncreasing reference to international law in the English courts has put pressure on established doctrines of English constitutional law”.Footnote 34 The relevant doctrines were parliamentary sovereignty, the primary vehicle through which democratic lawmaking is delivered within the state, and the separation of powers, which recognises that judges may be “ill equipped” or “ill suited” to determine questions concerning “foreign affairs”, “social policy” or “administrative feasibility”.Footnote 35 Both principles, Sales and Clement argued, “are deeply rooted in the modern polity in notions of democratic legitimacy, that it is for those representing the people in Parliament, and not the executive or the unelected judiciary, to make the law”.Footnote 36 The concern articulated by Sales and Clement was that a dilution of dualism – evidenced in increasing reliance on international law (particularly in relation to unincorporated treaties) in domestic litigation – was producing a destabilising effect on domestic constitutional arrangements.
By contrast, our argument is that the complexity of the relationship between the UK domestic and international legal orders is better understood as a feature of domestic constitutional law, rather than as a bug to be fixed by reversion to or insistence on dualist orthodoxy. Dualism, we suggest, overlooks the complexities of the relationship between domestic and international law and offers an at best rudimentary explanation of international law’s place in the UK constitutional order. The better view, we contend, is that the relationship is fragmented and dynamic: that is, it comprises multiple moving parts that do not cohere or fit into a neat, explanatory concept. In the three subsections to follow we outline dualism’s severely limited capacity as an explanatory notion.
A. Partiality
Dualism is traditionally presented as establishing a coherent link between the domestic and the international.Footnote 37 A number of considerations, however, suggest a qualified understanding of “absolutist” dualismFootnote 38 and that the concept provides only a partial account of relationships between rules of domestic and international origin.
The core of the dualist principle has recently been endorsed by the UK’s highest court. In SC the Supreme Court addressed whether provisions of the UN Convention on the Rights of the Child might be effective in domestic law via the jurisprudence of the European Court of Human Rights (considered pursuant to the Human Rights Act 1998).Footnote 39 Adopting a “strict” dualist view,Footnote 40 a unanimous Supreme Court was uncompromising: “[t]he only treaty to which the Human Rights Act gives domestic legal effect is … the Convention.”Footnote 41 The decision purportedly “corrected” a significant set of earlier Supreme Court judgments on the extent to which courts can have regard to unincorporated treaties when applying and interpreting domestic law,Footnote 42 effectively reinstating principles of non-justiciability and “no direct effect”.Footnote 43 In one sense and as Lord Sales has confirmed extrajudicially,Footnote 44 this “correction” can be viewed as a restatement of dualist orthodoxy. The fact that the Supreme Court deemed corrective action to be necessary, however, suggests instability in the domestic/international law relationship.
Beyond this core of dualism, a fragmentation of the principle is evident. While the direct effect of unincorporated treaty norms is precluded on an orthodox dualist approach, the domestic system appears to remain open to the “softer” influences of unincorporated treaties. So while unincorporated treaty norms may be non-justiciable and lack direct effects, they may, nonetheless, exert influence on domestic judicial reasoning.Footnote 45 In the application of domestic law, for instance, “there is a strong presumption in favour of interpreting English law (whether common law or statute) in a way which does not place the United Kingdom in breach of an international obligation”.Footnote 46 This “well established” presumption,Footnote 47 in favour of domestic law’s consonance with the UK’s international obligations, is complemented at common law by the more specific principle that “[d]evelopments of the common law should ordinarily be in harmony with the United Kingdom’s international obligations and not antithetical to them”.Footnote 48 The case law also recognises that a court may refer to international legal obligations as a means of “resolv[ing] ambiguities in the common law”.Footnote 49
The Supreme Court’s position on these softer influences is unclear. The decision in SC, for instance, made no reference to these principles when rejecting earlier suggestions that the traditional approach to unincorporated treaties should admit of a UNCRC exception.Footnote 50 The more recent Supreme Court decision concerning the competence of the Scottish Parliament in relation to the Scottish Government’s proposed independence referendum bill, however, contained the following passage concerning self-determination in international law:
The strong presumption in favour of interpreting our domestic law in a way which does not place the United Kingdom in breach of its obligations in international law is well established. […] If there is ambiguity in a statutory provision operating in a field where the United Kingdom is bound by a treaty obligation, the presumption of conformity with international law will apply to the interpretation of that statutory provision […]. This presumption of compatibility extends to international treaty obligations whether or not they have been implemented into domestic law within the United Kingdom.Footnote 51
While unincorporated treaty provisions are not directly effective in domestic law, they may, as Lord Sumption outlined in Belhaj v Straw, be put to a range of uses:
English law has always held to the dualist theory of international law. In principle, judges applying the common law are not at liberty to create, abrogate or modify municipal law rights or obligations in accordance with unincorporated norms derived from international law, whether customary or treaty-based. But, as Lord Bingham pointed out in R. v Lyons … international law may … affect the interpretation of ambiguous statutory provisions, guide the exercise of judicial or executive discretions and influence the development of the common law. Although courts are not bound, even in these contexts, to take account of international law, they are entitled to do so if it is appropriate and relevant.Footnote 52
Whilst not directly effective or justiciable unincorporated treaty provisions can, on this basis, safely be regarded as at least potentially influential.
Beyond these treaty-related questions, dualism provides an incomplete account of the relationship between the UK domestic constitutional order and the sources of international law. As already suggested, the UK’s dualism variant most clearly opposes the direct effect (absent statutory incorporation) of treaty norms. Customary international law (CIL), by contrast, may not require explicit statutory incorporation in order to enjoy domestic legal effect. Blackstone’s view – that the “law of nations” should be regarded as being “adopted in its full extent by the common law”Footnote 53 – has found some support in the courts.Footnote 54 In Trendtex – a 1977 case on the domestic status of contemporary CIL on state immunity – Lord Denning recognised “the doctrine of incorporation … [which] says that the rules of international law are incorporated into English law automatically and considered to be part of English law unless they are in conflict with an Act of Parliament”.Footnote 55 The idea that CIL norms are automatically incorporated into domestic law absent conflict with primary legislation contrasts with the argument that treaties remain outside the domestic legal order absent positive parliamentary incorporation. The common law position that CIL norms are part of domestic law may be an exception to a “strict” dualist analysis, because of an underpinning presumption that CIL has domestic legal effect. It is simultaneously the case, however, that Lord Denning’s recognition of parliamentary supremacy through the language of “conflict” allows for the maintenance of an essentially dualist position in which contrary statutory direction will displace that underpinning presumption. Everything depends on the degree of “automaticity” in the Trendtex position and recent cases – Keyu foremost amongst them – are at best opaque on that point.
Lord Mance’s analysis in Keyu suggests that the incorporation of CIL may not be as automatic as it might previously have seemed to be.Footnote 56 Commenting that “[t]he position is … somewhat more nuanced than Lord Denning MR’s statement [in Trendtex] might suggest”,Footnote 57 Lord Mance, “speaking generally”, expressed the view that “the presumption when considering any such policy issue is that CIL, once established, can and should shape the common law, whenever it can do so consistently with domestic constitutional principles, statutory law and common law rules which the courts can themselves sensibly adapt without it being, for example, necessary to invite Parliamentary intervention or consideration”.Footnote 58
“Shap[ing] the common law” is not the same thing as being automatically incorporated into it and framing the issue as one of “policy” suggests a move away from doctrine. This move is broadly consistent with Lord Bingham’s view – expressed in the earlier decision of R. v Jones – that “[customary] international law is not a part, but is one of the sources, of English law”.Footnote 59
In Freedom and Justice, however, the Court of Appeal took pains to maintain something close to the Trendtex position,Footnote 60 noting the “obiter” character of Lord Mance’s observations on the “presumption”.Footnote 61 The Court of Appeal concluded that “[t]he presumption is that a rule of customary international law will be adopted into the common law without the need for legislative intervention unless there is some positive constitutional principle which would prevent this”.Footnote 62
The Court of Appeal also seemed keen to avoid a “policy issue” approach, quoting Lord Mance’s observations on the “presumption” and reformulating them in these terms:
The presumption is that a rule of customary international law will be taken to shape the common law unless there is some positive reason based on constitutional principle, statute law or common law that it should not … The presumption reflects the policy of the common law that it should be in alignment with the common customary law applicable between nations. The position is different from that in relation to unincorporated treaty obligations, which do not in general alter domestic law.Footnote 63
The Court of Appeal’s suggestion that there is a “policy” of “alignment” between the common law and CIL is at odds with the “policy” logic of Lord Mance’s “presumption”. Lord Mance’s “presumption” operates to inform judicial decision-making on the “policy issue” of any particular CIL rule’s domestic legal effect. On that approach, any CIL rule can only be said to be part of the common law with confidence once a court has decided so. Further, when making a decision on that issue, Lord Mance’s “presumption” only operates where consistency with the existing domestic law position can be established (“whenever it can do so”): that is, there is no free-standing presumption of consistency or “alignment” (and the absence of that presumption from Lord Mance’s dicta explains the Court of Appeal’s decision to add its observations on the “policy of the common law”). The Court of Appeal, by contrast, presumes “alignment” on the basis of what it deems to be “the policy of the common law”.
The uncertain relationship between Trendtex, Keyu and Freedom and Justice reflects a fragmented, complex and dynamic relationship between UK domestic and international legal orders. On one view – the Court of Appeal’s dualist view in Freedom and Justice – the position is simple, coherent and stable. For all practical purposes CIL norms are automatically incorporated into domestic law apart from in the rare case where such incorporation presents a constitutional difficulty and that was, in any event, always the case on a proper reading of Trendtex. On another view – that suggested by Lord Mance in Keyu – CIL incorporation is now a complex “policy issue”, Trendtex incorporation is not necessarily the doctrinal position and Trendtex’s apparent clarity has fragmented into an uncertain, dynamic and unstable position which can only be resolved on a case-by-case basis as the courts work their way through the CIL norms that come before them.
The majority judgment in the Supreme Court’s March 2023 Law Debenture decision reviewed Keyu and Freedom and Justice. Footnote 64 Glossing Lord Mance’s “presumption” it noted that “given the generally beneficent character of customary international law, the presumption should be in favour of [CIL’s] application”.Footnote 65 Freedom and Justice was described as “highlight[ing] the complexity of the relationship of international law and municipal law within the United Kingdom”.Footnote 66
The case concerned Ukraine-Russia relations from late 2013 to November 2021 (so, pre-dating Russia’s 2022 full-scale invasion of Ukraine), with a specific focus on a 2013 arrangement through which Russia effectively loaned money to Ukraine.Footnote 67 Ukraine argued that the application of English contract law (the law governing the loan) should be informed by CIL on countermeasures.Footnote 68 The Supreme Court decided that the issue was not justiciable because, if it were, “national courts would become the arbiter of inter-state disputes governed by international law which is not their function”.Footnote 69 On this basis, and despite vague, obiter comments on Keyu and Freedom and Justice (as noted above), the Supreme Court made no actual decision on the domestic legal effect of CIL. It will, it seems, have to return to the uncertain inter-relationship between Keyu and Freedom and Justice at a later date.
Beyond dualism’s core concern with incorporation, decisions in relation to the “softer” influences of treaty norms and the domestic relevance of CIL norms suggest that international law’s place and effect in domestic law may be a question of context rather than doctrine. Mance L.J., as he then was, made this point in Ecuador v Occidental: “English courts are not … wholly precluded from interpreting or having regard to the provisions of unincorporated treaties. Context is always important.”Footnote 70
B. Hybridity
Recent experience suggests that dualism’s binary distinction between the domestic and the international may be misleading, and that international and domestic laws are often “enmeshed in ways that are sometimes elided by a rigid focus on formal doctrines”.Footnote 71 Some qualification of dualism’s seemingly strict insistence that a treaty provision only enjoys domestic legal effect if Parliament has provided for it in legislation seems necessary.
The effects of the UK’s membership of the EU and, to a lesser degree, the influence of Convention rights under the Human Rights Act 1998, suggest a form of legislative incorporation that creates a dynamic relationship between international and domestic laws. Within this dynamic relationship post-incorporation changes at the international level can translate into the domestic legal order without further legislative action. Section 2(1) of the European Communities Act 1972 initially facilitated this in relation to EC laws (as they then were), providing that the rights and remedies available “from time to time” by virtue of the EC treaties would be “without further enactment … given legal effect or used in the United Kingdom”. The characterisation – by the Supreme Court in Miller 1 – of this feature of the European Communities Act 1972 as providing the “‘conduit pipe’ through which EU law [was] introduced into UK domestic law”Footnote 72 can be seen as a modification of dualist orthodoxy. As Gavin Phillipson has summarised, the European Communities Act 1972 allowed “a foreign source of law to pour directly into UK law and take effect as domestic law”.Footnote 73 The consequences of this domestic accommodation of EU law principles, via the European Communities Act 1972, were – as the majority in the Supreme Court decision in Miller 1 recognised – “unprecedented”: “[the European Communities Act] authorises a dynamic process by which, without further primary legislation (and in some cases, even without any domestic legislation), EU law not only becomes a source of UK law, but actually takes precedence over all domestic sources of UK law, including statutes.”Footnote 74
If dualism is to operate as a safeguard for domestic institutions then this marginalisation of Parliament’s incorporating role challenges the orthodox, Parliament-centred account.Footnote 75 Within the European Communities Act model, once the relevant treaties were incorporated, the domestic oversight or filtering role associated with an orthodox dualist account was significantly curtailed. This point is reinforced by the suggestion – also by the majority in Miller 1 – that during EU membership “the EU Treaties, EU legislation and the interpretations placed on these instruments by the Court of Justice” effectively operated as “direct sources of UK law”.Footnote 76
This model of “dynamic” incorporation partially persists following the UK’s exit from the EU. Section 7A of the European Union (Withdrawal) Act 2018 adopts the same “without further enactment” formula as section 2(1) of the 1972 Act in order to give effect to the terms of the European Union Withdrawal Agreement. This residual alignment between domestic and EU laws is perhaps most visible in the post-Brexit arrangements for Northern Ireland, which preserve a connection (detailed in the Northern Ireland Protocol and Windsor Framework) in respect of EU laws integral to upholding the Belfast/Good Friday Agreement.Footnote 77 While Brexit itself may be a political act or process, designed to reverse some of the integration between domestic and international legal orders, the legislative mechanisms employed to achieve this reversal – as section 7A illustrates – do not revert to dualist orthodoxy. As much was implicitly acknowledged by the Supreme Court in Allister: “whilst ordinarily under our dualist system international law and domestic law operate in independent spheres, this treaty between the UK and the EU [the Withdrawal Agreement] was to form part of UK law and give rise to legal rights and obligations in domestic law.”Footnote 78 The Withdrawal Agreement is therefore the prompt for a continued, albeit limited,Footnote 79 form of dynamic alignment with the EU.
In terms of method if not effect,Footnote 80 a similar interaction between the domestic and international legal order is envisaged by the Human Rights Act 1998. This is clear on the face of the Act, which requires that decisions of the European Court of Human Rights – “whenever made or given” – must be “taken into account” in domestic adjudication concerning a Convention right.Footnote 81 This stipulation envisages post-Human Rights Act judgments of the Strasbourg Court enjoying the same status as those decided prior to the Act’s implementation. It follows that domestic human rights law following the Human Rights Act 1998 develops in symbiosis with the Convention and its attendant case law. A fluid element to the Human Rights Act’s domestication of the Convention rights is the indirect consequence of section 2(1), which – to a potentially variable degree – ties the rights protected in municipal law to the “dynamic and evolutive”Footnote 82 jurisprudence of the European Court of Human Rights.Footnote 83 The “incorporation” of the Convention rights on the Human Rights Act model clearly envisaged a mutability in the development of the Convention jurisprudence, handing domestic courts the task of “keep[ing] pace” with the Strasbourg Court.Footnote 84
The senior courts have acknowledged this interdependence and further recognised that the purpose of the Human Rights Act is to give “effect in domestic law to an international instrument … which [can] only be authoritatively interpreted by the Strasbourg court”.Footnote 85 This approach in turn views the substantive rights,Footnote 86 and remedial extent,Footnote 87 of the Act as developing in tandem with developments in the jurisprudence of the European Court of Human Rights. In the Human Rights Act context the domestic filter is managed by the courts, who – via their section 2(1) obligation – have the means to regulate the domestic law impact of the Strasbourg case law. This filter, as is well known, however, is conditioned by the courts’ position under the Act as “public authorities” charged with acting consistently with the Convention rights,Footnote 88 and vis-à-vis the “authoritative” interpretative function of the European Court of Human Rights. As such, the operation of the section 2(1) “filter” has tended towards an approach to the Convention rights in domestic law which is generally led by, and responsive to, development of those rights by the Strasbourg Court.Footnote 89 Attempts to explain the Human Rights Act via an orthodox dualist account – as a municipal statute giving rise to “domestic rights” which fall to be interpreted by “domestic courts”Footnote 90 – fail to capture the necessary (ongoing) linkage between the rights given effect by the Act and the developing jurisprudence of the European Court of Human Rights. As with the European Communities Act before it, the Human Rights Act operates as a “conduit” through which the potentially variable requirements of the Convention rights are translated into domestic law.
It is clear from the above illustrations that, while Parliament may have stipulated that certain external norms should permeate the domestic constitution, the UK’s membership of the EU and the domestic application of Convention rights effectively abridged Parliament’s filtering role in relation to post-“incorporation” norms originating in EU institutions and the European Court of Human Rights. A dilution of the dualist principle is, therefore, apparent in this dynamic, “conduit” method. If these EU and ECHR examples evidence a modified dualist methodology – a “conduit” rather than binary approach – then the hybrid nature of the law that results from this dynamic mode of “incorporation” must be recognised.
This hybrid body of law amalgamates elements drawn from the domestic and international legal orders. The intersection of the domestic and the international is illustrated by the fact that the impact of EU norms in UK law owe(d) much to EU law doctrines of supremacy and direct effect. Those doctrines formed the backbone of a “legal order … separate from that of each of the Member States but which substitutes itself partially for those in accordance with the rules precisely laid down in the Treaty itself and which consist in a transfer of jurisdiction to Community institutions”.Footnote 91 Despite suggestions that “[a]ny attempt to interfere with primary legislation would be wholly unconstitutional”,Footnote 92 the supremacy of directly effective EU law was, ultimately, recognised as requiring the disapplication of inconsistent domestic statute.Footnote 93 In this way EU law operated outside or beyond the limits of dualism’s parliamentary filter.
Although Brexit formally ended the supremacy of EU law in the UK legal order,Footnote 94 the residual influences of EU laws applicable in the UK during membership of the EU – particularly, for instance, across policy fields within the remits of the Department of Environment, Food and Rural Affairs and the Department for Transport – remain considerable.Footnote 95 Again, while at first glance the UK’s departure from the EU might appear to mark an undoing of the post-1972 integration of legal orders, the legal remnants of that integration – whether labelled “retained EU law” or “assimilated law” – are domestic only in the sense that statute directs that they should be regarded as such.Footnote 96 Divergence from what remains of EU laws’ influence is certainly visible and – as a result of the Retained EU Law (Revocation and Reform Act) 2023Footnote 97 – has recently reached a turning point.Footnote 98 But the dualist lens does not allow us to see the complex, post-Brexit legal landscape of “assimilated” law and the ongoing supremacy and direct effects of the Withdrawal Agreement clearly.Footnote 99
It is equally difficult to see the legal order created by the Human Rights Act 1998 in strict dualist terms. The Act underpins an alternative mode of “constitutional review”,Footnote 100 based, to a considerable degree, on the external influence of the European Convention on Human Rights and Strasbourg jurisprudence. Human Rights Act adjudication concerning the Convention rights is of a kind with adjudication for compliance with EU law in the sense that it permits primary legislation and public authority acts to be scrutinised for compliance with a set of constitutional standards that have non-domestic origins.Footnote 101 The Convention rights applicable by virtue of the Human Rights Act were not intended to simply function as an overlay to domestic law, nor – in the words of Laws L.J. – should the Strasbourg case law be treated “as if it were a compulsory adjunct taken from an alien source”.Footnote 102 Instead, those rights were to be “woven into” domestic law.Footnote 103 The Human Right Act’s effect in breaking down dualist division and initiating the domestic development of a body of cogenerated law is apparent in fields such as the protection of personal privacy where the pre-existing common law has become intertwined with the requirements of the Convention and its case law.Footnote 104 Quoting Lord Justice General Rodger’s comment that Convention rights “soak through and permeate the areas of law in which they apply”,Footnote 105 the Supreme Court has recognised this merging of the domestic and the international: “The [Human Rights] … Act does not … supersede the protection of human rights under the common law or statute, or create a discrete body of law based upon the judgments of the European court. Human rights continue to be protected by our domestic law, interpreted and developed in accordance with the Act when appropriate.”Footnote 106
The simplistic conclusion here is that decades of UK engagement with EU and ECHR norms broke down the dualist divide between the domestic and the international by bringing those spheres closer together. The more sophisticated take is that in both instances (EU and ECHR) statutory “incorporating” provisions only partially account for the domestic influence of norms with non-domestic origins and that the law produced out of the interaction between the domestic and the international must be understood as a cogenerated or hybrid product of that interaction. That product cannot, as the post-Brexit, EU law experience shows, easily be converted into something purely domestic.
C. Domestication
Dualism is claimed to provide stability and clarity. The dualist segregation of the municipal and international legal orders provides, it is suggested, vital insulation from the unpredicatible influences of rules which have not been incorporated, or filtered, by domestic institutions.Footnote 107 The previous section highlighted the modification of the approach taken by domestic law to this “filtering” process in the European Communities Act and the Human Rights Act. A related point, and the final ground on which to doubt the orthodox account of dualism, flows from this. Dualism encourages a view of incorporation as an event, the end point in a process of integration (the point at which the hitherto external norm is given domestic “justiciability” and “direct effect”) rather than the first step in a process of domestication.
“Incorporation” may resolve base-line questions about the potential applicability of a non-domestic norm in the domestic legal order, but it does not necessarily address deeper issues of what we might call constitutional habilitation. A pattern of post-incorporation uncertainty (and occasionally) resistance to the importation of the decisions or adjudicative techniques of international courts and international institutions runs through the discourse. Dualism does not express the receptiveness of the domestic constitution to international legal influences or capture the various processes by which international and domestic laws are linked and applied. Brief discussion of some examples illustrates the point.
In an EU law context UK courts were initially sceptical about domestic law’s ability to provide remedies capable of addressing inconsistencies between statute and directly effective European law. In the Court of Appeal’s Factortame (No.1) decision Lord Donaldson noted that there was “no juridical basis” in domestic law for the courts to suspend the operation of statute.Footnote 108 Lord Bridge echoed the point in the Appellate Committee of the House of Lords, suggesting that granting such a remedy would be “directly contrary to Parliament’s sovereign will”.Footnote 109 It took a reference to the European Court of Justice for these domestic concerns to yield to the (then) overrding imperative that in the event of irreconcilable conflict domestic law must give way to European law, given its superior status within the European Community framework.Footnote 110 Latterly, the Supreme Court’s HS2 decision saw Lords Neuberger and Mance hypothesising that the reach of EU law into domestic constitutional arrangements might not be limitless. The two justices, with whom the remaining five members of the Supreme Court agreed, noted that it was “certainly arguable … that there may be fundamental principles, whether contained in other constitutional instruments or recognised at common law, of which Parliament when it enacted the European Communities Act 1972 did not either contemplate or authorise the abrogation”.Footnote 111
Comparable discussions have taken place in the context of rights adjudication. Domestic judges have, for example, suggested that the section 2 Human Rights Act presumption, or Ullah principle,Footnote 112 that Strasbourg Court jurisprudence should be reflected in the decision-making of domestic courts, ought not to apply if following that jurisprudence would “compel … a conclusion fundamentally at odds with the distribution of powers under the British constitution”.Footnote 113 The Supreme Court has declined to follow Strasbourg case law where doing so would produce damaging domestic law consequences.Footnote 114 The Supreme Court has also suggested that unpersuasive reasoning by the Strasbourg Court may diminish the likelihood of its staightforward domestic application.Footnote 115 A series of Supreme Court decisions on common law rights sought to limit the applicability or relevance of Strasbourg case law where domestic law provides a rights-compliant response.Footnote 116 Each of these instances illustrates the post-incorporation uncertainties that fall to be resolved when domestic courts apply and interpret norms with non-domestic origins.
Application of the Convention’s legal standards via the Human Rights Act has also provoked some judicial concern. The potential “powerlessness” of domestic courts faced with a clear and applicable decision of the Grand Chamber of the European Court of Human Rights is apparent in Lord Rodger’s observation, in Secretary of State for the Home Department v AF, that “[e]ven though we are dealing with rights under a United Kingdom statute, in reality, we have no choice: Argentoratum locutum, iudicium finitum – Strasbourg has spoken, the case is closed”.Footnote 117 The Supreme Court has occasionally expressed its frustration at perceived deficiencies in Strasbourg decision-making – suggesting occasionally unprincipledFootnote 118 and “incoherent”Footnote 119 reasoning – as well as in relation to the court’s “expansionist”Footnote 120 reading of the Convention.Footnote 121
Working within the framework of the Act, ECHR influences have led to increased use of proportionality analysis in judicial review cases. The influence of proportionality has prompted concern that courts are moving away from the procedural focus of judicial review towards merits-based review.Footnote 122 This, in turn, has led to debate over whether the domestic Wednesbury standard should give way to the “more precise and more sophisticated” requirements of proportionality analysis.Footnote 123 For some the proportionality test is nothing more than a disruptive “continental” interloper: “[t]here is no doubt that in the world of judicial review proportionality has advanced like a cuckoo, occupying the common law nest of traditional assessment, laying its continental eggs in it, and ejecting its home-incubated Wednesbury hatchlings.”Footnote 124
These examples suggest that the dualist worldview – the separated spheres account of domestic and international law – conditions the national reception of “incorporated” norms, such that a sense of separation (or otherness) persists even after “incorporation”. Lord Neuberger characterised this concern in the pre-Brexit era as rooted in tension between legal traditions and in a sense that “that UK law, and in particular the common law, is being subjected to undesirable mainland European civilian law influences, from the jurisdiction of the Court of Justice of the European Union, the CJEU in Luxembourg and of the European Court of Human Rights, the ECtHR in Strasbourg”.Footnote 125 The resulting instability caused by this tension is perhaps most obviously apparent in political objections to extra-jurisdictional influences. As a case in point, resistance to the domestic effects of decisions by EU institutions (e.g. the Court of Justice of the EU) was fundamental to pro-Brexit efforts to “take back control” of lawmaking powers.Footnote 126
The Human Rights Act, as discussed above, amplifies the significance of Strasbourg decision-making for domestic adjudication. That has led to complaints, similar to those made in relation to EU influences, that domestic institutions are somehow subjugated to non-domestic influences.Footnote 127 In both instances (EU and ECHR) Parliament directed that the relevant norms were domestically applicable. That did not, however, prevent debate or controversy about the domestic reception of international legal norms and decision-making. The domestication of international law is, as the above decisions illustrate, an iterative process. Whilst incorporation is a vital point in an international norm’s transition into the domestic legal order it clearly does not put a definite end to debate about a non-domestic norm’s domestic effect or its relationship with other domestic laws and principles.
IV. Imposing Dualist Coherence/Recognising Fragmented Complexity
One possible response to these tensions is to recognise that constitutions are not hermetically sealed,Footnote 128 and that dualism is a variable rather than an absolute concept. Feldman, for one, acknowledges that dualism operates as a “semi-permeable membrane, which allows rules to pass through it in different directions for different purposes”.Footnote 129 Similarly, Poole draws a distinction between the orthodoxy of “strict dualism” and the practical realities of the fluid interplay between domestic and EU laws to which the UK’s EU membership gave rise, arguing that “[s]trict dualism miss[ed] what [wa]s distinctive about the ECA”,Footnote 130 namely, that “a dynamic, international source of law was grafted onto, and above, the well-established existing sources of domestic law: Parliament and the courts”.Footnote 131 Some uncertainty about how domestic law relates to international law seems inevitable. Yet the degree of fragmentation mapped in the previous sections suggests, we argue, that dualism’s binary opposition of the domestic to the international is becoming redundant.
We noted above that the relationship between domestic and international laws provides an indicator of constitutional identity. This final section reflects on the fragmentation of dualism as a reflection of broader constitutional patterns. Cheryl Saunders has observed that:
By its very nature, as the law that binds the organs of state, public law is closely tied to the politics and political culture of the state in which it is embedded. Public law claims to derive its legitimacy from the people of a state, at least as a matter of theory and rhetoric. In practice, public law undeniably depends in some degree of acceptance by political elites.Footnote 132
In the UK’s (in)famously political constitution,Footnote 133 it stands to reason that the tides of political opinion will impact upon the shape and tone of public or constitutional law. As such, it is in a sense elementary that political tensions concerning the extent to which non-domestic norms permeate the domestic constitution will influence perceptions of the legal position.
Doubts about the domestic influence of norms generated outside the national legal order are a leitmotif in a number of recent, constitutionally significant political initiatives. Foremost among them, the Brexit process is a textbook example of a politico-legal project centred on the dismantling of linkages between the domestic legal order and international legal influences. Recurrent efforts to reform the UK’s human rights framework – or alternatively for the UK to withdraw from the Convention system – are heavily influenced by concerns about the extent to which the European Court of Human Rights and its jurisprudence influences and constrains domestic law and domestic decision-making.Footnote 134
While Brexit and possible Human Rights Act reforms exemplify the tensions, they are not the only symptoms of this “exceptionalism”. Efforts to redefine and diminish international law’s place in the domestic legal order range from the relatively subtle – such as the removal (between 2015 and 2024) from the Ministerial Code of explicit reference to ministers’ obligations to act consistently with “international law and treaty obligations”Footnote 135 – to the harder-edged. The United Kingdom Internal Market Bill was (notoriously) intended, in its original form, to “break international law in a specific and limited way”.Footnote 136 While the bill was not enacted in its original form the message was that the UK’s international legal obligations – even those contained in a recently-agreed treaty – were open to avoidance under cover of Parliament’s (domestic) legislative sovereignty.
Conventional dualist debate centres on how international norms are domesticated and includes recognition of a possible “dissonance” between the UK’s obligations in international law and the requirements of domestic law.Footnote 137 More recent developments highlight a growing debate about whether international norms should be domesticated at all and whether the effects of any past domestication should be curtailed. This creates a particular dissonance, within the domestic legal order, between those who take the view that domestic law has a necessary if dynamic connection with international law and those who take the view that domestic law is and must be domestic.
The most striking legislative examples of this dissonance – and these are by no means the only relevant examplesFootnote 138 – relate to legal disputes arising out of conflict situations and control of the UK’s borders. Legislation limiting legal actions against UK military personnel in relation to actions outside the UK,Footnote 139 and limiting criminal prosecutions and civil proceedings relating to the conflict in Northern Ireland,Footnote 140 attempt to restrict the domestic influence of ECHR norms applicable under the Human Rights Act, arguably in violation of the UK’s obligations under the Convention.Footnote 141 The enactment of the latter statute – the Northern Ireland Troubles (Legacy and Reconciliation) Act 2023Footnote 142 – prompted the Government of Ireland, in January 2024, to make an interstate application to the European Court of Human Rights on the basis that that the Act breaches a number of Convention articles.Footnote 143 In Dillon the Northern Ireland High Court made declarations of incompatibility in relation to the Act’s immunity from prosecution provisions (on the basis that they conflict with the requirements of Article 2 and 3 ECHR) and in relation to the Act’s limitations on civil procedings arising out of the troubles (in light of their incompatibility with Article 6 ECHR).Footnote 144
In the context of border controls, efforts to “stop the boats” via the Illegal Migration Act 2023 and initiatives relating to the Rwanda deportations policy,Footnote 145 employ a range of devices designed to avoid the effects of the UK’s domestically applicable, international human rights obligations. The Illegal Migration Act 2023 (IMA) has been argued to run contrary to a “sizeable proportion of the UK’s obligations under international human rights law” including those that are domestically applicable by virtue of the Human Rights Act.Footnote 146 The IMA insulates itself from potential judicial interpretation designed to achieve compatibility with Convention rights by declaring that section 3 of the Human Rights Act “does not apply” to its provisions or any provisions made “by or by virtue of” the IMA.Footnote 147 The Safety of Rwanda (Asylum and Immigration) Act 2024 – enacting the legislative fiction that Rwanda is a safe country for deportation purposes – similarly purports to exclude the application of the Human Rights Act to its terms and prospective operation, specifically disapplying almost all of the Human Rights Act’s operative provisions, including section 2 (the duty on domestic courts to “take into account” Convention case law in domestic human rights litigation), section 3 (the Act’s interpretative provision) and section 6 (the obligation on public authorities to act consistently with the Convention rights).Footnote 148
In short, the UK Government and Parliament has proposed and, in some cases, adopted a series of international law avoidance mechanisms which either reduce or destroy the domestic effect of domestically applicable norms or exclude the potential domestic influence of the UK’s broader international obligations. The culmulative effect of these legislative measures is twofold. In a straightforward sense legislative disapplication of the Convention rights partially reinforces dualist orthodoxy by illustrating that international obligations remain contingent on statute for their domestic effects; statute can take away, as well as grant, domestic legal effect. More pertinently however, the legislative disapplication of otherwise “incorporated” international norms demonstrates dualism’s growing redundancy as a concept that explains the UK domestic/international law relationship. Legislative differentiation of contexts or circumstances in which “incorporated” norms will and will not apply further undermines the binary distinction on which dualist orthodoxy rests. Such differentiation fragments the dualist concept and – given the extent of recent political contestation over connections between international and domestic laws – shows the potential for what remains of that idea to collapse into, rather than bring shape and order to, fluctuations in the domestic political climate.
The “messiness” and “disagreement” that characterises recent aspects of the relationship between the UK and international legal orders reviewed in this section can, perhaps, be explained away as by-products of the UK’s political constitution.Footnote 149 Dualism’s (supposed) requirement for legislative incorporation might, equally, be said to reflect a political constitutional preference for democratic lawmaking primarily delivered by statute. This emphasis on political explanation does, however, risk reaching for “the political” because of its perceived capacity to simplify the complexities of “the legal”. If the object of inquiry is the relationship between the UK domestic and international legal orders then the focus needs to remain on the specifics and particulars of that relationship, as they play out in specific judgments, statutes and other legal materials.
Our broad point is that no simple, neat explanatory concept can account for the complex, fragmented and dynamic nature of the actual relationship between the UK domestic and international legal orders that plays out in particular cases, situations and documents. A political constitutional analysis might suggest that the power to determine the domestic legal effect of a treaty norms rests with Parliament. The case law, however, shows that Parliament is often not as clear about its intentions as a judge faced with a relevant question might like.Footnote 150 Broad propositions about the allocation of constitutional power have little practical impact if the judge finds it difficult to discern Parliament’s will on the relevant point. If we are, then, concerned with the actuality of the relationship between domestic and international law our focus has to be on its granularity, its specifics, rather than on structural abstractions that offer palatable simplicity at the expense of addressing real and persistent complexities.
Alternative concepts which have been advanced as offering some explanation for the relationship between international and national legal orders also appear inapt in this context. Global constitutionalism, for instance, suggests that the boundaries between national and international legal orders have been weakened by the emergence of a transnational body of rules, with a particular focus on the protection of human rights.Footnote 151 Allusions to that idea may occasionally be visible in UK constitutional discourse,Footnote 152 but global constitutionalism per se is at odds with recent UK constitutional practice. The Supreme Court’s decision in SC is an outright rejection of any suggestion that treaty-based human rights obligations – beyond those explicitly incorporated by statute – have any particular domestic status or effect.Footnote 153 The Safety of Rwanda (Immigration and Asylum) Act 2024 is a strident assertion of Parliament’s capacity to insulate domestic decision-making from scrutiny on the basis of “any … international law, or convention or rule of international law, whatsoever”.Footnote 154 International human rights law and a broad sense of global interconnection are the very foundations of any global constitutional analysis. Any suggestion that the UK domestic legal order is built on that kind of constitutionalism is defeated by the clear evidence in SC and the 2024 Act.
Constitutional pluralism, meanwhile, maintains that hierarchies in national constitutional law have given way to a more heterarchical understanding of interlocking legal systems.Footnote 155 Again, we can see some affinity between this idea and the suggestion that the precise impact of an international norm in the domestic legal order is a matter of context rather a function of doctrine. Equally, the UK’s period of EU membership produced illustrations of pluralist thinking from domestic judges attempting to grapple with laws originating from competing sites of constitutional authority.Footnote 156 As with the notion of global constitutionalism, however, recent domestic developments are inconsistent with constitutional pluralism as a means of explaining the relationship between the UK domestic and international legal orders. The UK’s departure from the EU indicates a partial retreat towards a “classic dualist” position in which “alien norms … are valid only through the recognition of, and to the extent permitted by, the state legal order”.Footnote 157 As such, the UK’s legal order – though able to accommodate alternative sources of law and authority – displays a clear preference for doing so without conceding that the hierarchies resulting from parliamentary sovereignty are diminished; as legislation has recently emphasised, “the Parliament of the United Kingdom is sovereign”.Footnote 158
As lenses, global constitutionalism and constitutional pluralism make something of the relationship between the UK domestic and international legal orders visible. Yet neither concept offers a complete account of the relationship and, in our view, no single lens or explanation can do so. We suggest that the fragmented, complex, dynamic nature of the relationship confounds attempts to find a “catch-all” explanation.
V. Conclusion
With the creation of a statutory framework that facilitates the UK diverging from the residue of EU legal influences that remain after Brexit,Footnote 159 the idea that the post-Brexit constitution is reverting or might revert to earlier, simplistic and binary orthodoxies is, perhaps, instinctively appealing. Our analysis, however, highlights the complexities of the so-called “dualist” constitution and points towards an increasingly fragmented, complex and dynamic relationship between the domestic and international legal orders that does not accord with, and cannot fully be explained by, the orthodox dualist account. Cases concerning CIL and unincorporated treaties suggest a dualism more dynamic than stable. The hybrid products of the UK’s interactions with European legal orders defy dualist categorisation, owing their content to a combination of domestic and international sources. The binary distinction on which dualism rests is complicated by the intricacies of post-“incorporation” processes of domestication. The straightforward appeal of a reversion to dualist orthodoxy – of precisely the kind endorsed by the Supreme Court in SC – fades in the face of such difficulties, precisely because the picture is not simple or binary but complex and multi-dimensional.
These illustrations of a fragmented relationship are components of (or, at least, run parallel to) a seam of resistance to or scepticism about the place of international legal norms, institutions and processes in the UK’s domestic legal order. The emerging picture is of a UK legal order less integrated with, and potentially more opposed to, the international legal order than had previously seemed to be the case. Collectively, these pressures highlight dualism’s inability to account for the realities of the UK’s relationship with international law. What comes next is, of course, a primarily political question and it seems the UK’s new (2024) Government intends to take a less oppositional approach to international legal obligations than has been apparent in legislation, reviewed in the previous section, passed under recent governments.Footnote 160 If it does so the lesson to be taken from our analysis in this article may be that dualism, if not wholly redundant, is, at best, a flawed and incomplete guide to the intricacies of the relationship between UK domestic law and international law.
In closing, then, our analysis distils into three key points. First, dualism does not and cannot account for the entire relationship between the UK domestic and international legal orders. Second, the complex picture of the relationship emerging from our analysis should be accepted on its own terms, without any attempt to simplify or compress it into some “new” explanatory concept. Third, and notwithstanding any practical utility that a “new” explanatory concept might be thought to have, the picture of the relationship offered in this article provides a more realistic and comprehensive appraisal of the complex, fragmented and dynamic constitutional landscape than any such explanatory concept can offer.
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