When politics trumps strategy: UK-EU security collaboration after Brexit

Both the United Kingdom (UK) and the European Union (EU) have significant incentives for close collaboration in foreign, security and defence policies, given their shared strategic interests, the clear potential for efficiency savings in working together, and the intensity of prior working relations. That the recently negotiated EU–UK Trade and Cooperation Agreement contains no provisions in this area is thus puzzling for followers of European security, who predicted prompt agreement, and for theories of international cooperation, which emphasise the importance of shared threats, absolute gains and prior interaction. We argue the failure to reach such an agreement stemmed from the politics of the withdrawal process itself, which resulted in acute problems of institutional selectivity, negotiating dynamics that polarised the relationship, institutional change that made an agreement less likely, and distributional scrabbling to supplant the UK. Our findings show that the dynamics of moving away from existing forms of cooperation are highly distinct from those motivating cooperation in normal times.