What is the common point between Shamima Begum, Nazanin Zaghari-Ratcliff and the one million British citizens in the EU ?Whatever their (many) differences, all raise the question of what a state’s obligations are towards its citizens abroad.

The fate of UK citizens in the European Union in a Brexit context is perhaps not the biggest issue on the Brexit agenda and, as a potential stumbling block, it seems dwarfed by the ‘backstop’ – but it does raise deeper questions about how large their interests should loom in the negotiation process.

By committing to pull out of the European Union, the UK has potentially significantly impaired the situation of those expatriates, a useful reminder that diasporas are exposed to the decisions of their home country and often on the frontline of other countries’ reaction to it. Of course, there was never an acquired right to European citizenship, but does the UK have special duties to seek to mitigate the harm inflicted on that group, given some of the increasingly evident human rights implications of residency status?

There is a long tradition in international law of the protection of one’s citizens abroad (or “aliens” as they were often known in the host country). The state was seen to be protecting its own sovereign interests when it intervened on behalf of its expatriates (for example as part of diplomatic protection), rather than expatriates having a particular cause of action against their sovereign. But this may be changing slowly as a result of human rights and a sense that expatriate citizens are not only the ‘objects’ of their sovereign’s solicitude but rights bearers and active political subjects.

Of course, British citizens in the European Union are not in need of ‘protection’ stricto sensu (one would hope), but they are in need of diligent representation. In rhetoric that seems to underscore both the reality and the limits of the UK’s obligations, it has insisted that although it “cannot act unilaterally to protect the rights of UK nationals in the EU, (…) it will take necessary steps where possible to support UK nationals.”

Interestingly, the European Union itself, of which British citizens are for a while longer at least citizens, has done its part, calling upon member States to ensure their continued legal residence in a variety of ways in case of ‘no deal.’ Although retaining residence rights in the country where they are already settled is clearly on the agenda, British nationals do stand to lose European mobility rights.

Note that the issue is both facilitated and potentially complicated by the fact that the fate of British citizens in the EU is closely intertwined with that of EU citizens in the UK: British citizens in the EU stand to either benefit from or be penalized by whatever deal the UK is willing to give EU residents. It is noteworthy that, in case of a no-deal scenario, the UK has insisted that it would facilitate its citizens’ return, for example by ensuring access to health care and benefits, although this may seem a poor substitute for full EU rights.

Indeed, organizations representing British expatriates in the EU have at times claimed that they felt betrayed and actively militated for a better deal, in ways that underscore their continued agency in the making of any Brexit deal. Going forward, it seems that it will be ever more difficult for states to ignore such extra-territorial constituencies.

Frédéric Mégret is a Professor at the Faculty of Law, McGill University. He is currently writing a book with Larissa van den Herik of the University of Leiden for CUP on “Aliens, Diasporas and International Law”. He is also the author of, “Transnational Mobility, the International Law of Aliens, and the Origins of Global Migration Law”, which featured in the AJIL Unbound symposium on Framing Global Migration Law. All content published in AJIL Unbound is available to read free of charge.