No member state has been as influential as the United Kingdom in shaping EU policies to fight serious crime, including terrorism. Paradoxically, no country has been more effective in blocking initiatives to have the EU play a role in defence. In both domains, the effects will be felt long after the UK has left the EU. This chapter discusses the UK's chequered legacy in European security policy, and how this may affect future cooperation. Will police forces and intelligence agencies continue to act in concert to mutual advantage, or – as will be argued below – are data exchanges and mutual assistance more likely to suffer? Will European military and security cooperation benefit from the UK's departure, or will the EU's credibility and effectiveness diminish? What measures could prevent unnecessary damage to European and British security?

This chapter proceeds in three stages. First the effects of Brexit on criminal justice cooperation will be assessed. The discussion then turns to the external dimension of foreign policy, security and defence. The final section reflects on repercussions for the future.

INTERNAL SECURITY

The United Kingdom played a leading role in shaping the EU's internal and external security policies. It was the 2005 British presidency that proposed, jointly with the EU Counterterrorism Coordinator, the EU's counterterrorism strategy, which still directs EU policy. The European Commission's first two directors for criminal law and justice were British (Adrian Fortescue, 1999–2003, and Jonathan Faull, 2003–10), as was the first president of Eurojust (Michael Kennedy, 2002–7). Rob Wainwright, a former Security Service (MI5) agent, directed Europol for nearly a decade (2009–18). Claude Moraes chaired the European Parliament's Committee on Civil Liberties, Justice, and Home Affairs (2014–19). Britain's last commissioner, Julian King (2016–20), was in charge of security. It is a record unmatched by any other member state.

Following Brexit, the UK will lose its voice in the institutions, preparatory committees and agencies that decide and implement EU security policy. It will be out of the room when the European Council, the Council, the Commission or the European Parliament set policy.