The exposure of two senior republicans as informers for British intelligence in 2005 led to a popular perception that the IRA had 'lost' the intelligence war and was pressurised into peace. In this first in-depth study across the entire conflict, Thomas Leahy re-evaluates the successes and failures of Britain's intelligence activities against the IRA, from the use of agents and informers to special-forces, surveillance and electronic intelligence. Using new interview material alongside memoirs and Irish and UK archival materials, he suggests that the IRA was not forced into peace by British intelligence. His work sheds new light on key questions in intelligence and security studies. How does British intelligence operate against paramilitaries? Is it effective? When should governments 'talk to terrorists'? And does regional variation explain the outcome of intelligence conflicts? This is a major contribution to the history of the conflict and of why peace emerged in Northern Ireland.

Winner, 2021 Brian Farrell Book Prize, Political Studies Association of Ireland

‘An important and difficult subject, explored with skill and in very impressive, well-researched detail.'

Richard English - author of Armed Struggle: The History of the IRA

‘Informers and agents are central to insurgencies. They can be devastatingly effective, yet inflict terrible suffering. Meticulously dissecting the intelligence war in different regions, Leahy's analysis of how informers and agents affected the strategic interaction between republicanism and the British state is a major contribution to scholarship on the Northern Ireland conflict.'

Huw Bennett - author of Fighting the Mau Mau: The British Army and Counter-Insurgency in the Kenya Emergency

'Thomas Leahy’s study of the Intelligence War in Northern Ireland draws on rich new evidence from the archives to provide a well-paced, thought-provoking and richly-textured account of the impact of British Intelligence measures during the conflict. The author makes a compelling case for analysing both military and political intelligence together and offers a fresh new perspective on why it took so long to bring an end to the violence through a negotiated peace settlement.'

Niall Ó Dochartaigh - author of From Civil Rights to Armalites: Derry and the Birth of the Irish Troubles

‘… sheds new light on how British intelligence used agents, informers, special-forces and surveillance in the city during the recent conflict.’

Kevin Mullan Source: Derry Journal

‘… this is a well-informed, competent, accessible and engaging assessment of the role of intelligence in the periods before the IRA ceasefires. It will be useful for scholars not just of the ‘Troubles’ but of the role that terrorist groups and their leadership, state political actors, the security forces and intelligence can play in progress towards peace.’

Samantha Newbery Source: Intelligence and National Security

‘… an easy read … this work should be recognised as a valuable contribution to our understanding of the Northern Ireland conflict and a timely disruption of a potentially dangerous consensus.’

Patrick Mulroe Source: History Ireland

‘Thomas Leahy’s The Intelligence War Against the IRA is an important new contribution to the growing, and changing, interpretations of The Troubles … a great addition to The Troubles canon. It is a well-researched study with a diverse range of secondary material, a wealth of archival evidence and interviews with significant figures on all sides of the conflict.’

Nick Clifton Source: History@Kingston

‘This well-researched and argued study will interest students of Northern Ireland, political violence, and counterinsurgency.’

A. H. Plunkett Source: Choice