UK involvement in the EU Area of Freedom, Security, and Justice (AFSJ) has been patchy. It never joined the Schengen border-free zone, and when in 2014 it exercised a block exit from all AFSJ measures, it selectively rejoined a substantial number. Even if partially outside, the UK has been a leader inside. Advanced intelligence capabilities meant it provided important support to the functioning of agencies such as Europol and UK laws inspired EU laws, for example, on data retention. The need to preserve some pragmatic forms of cooperation between the UK and the EU is obvious and shared by the UK security establishment. There is a partial institutional precedent . When Denmark rejected participation in Europol in a popular referendum, the Danish government obtained a deal from the EU institutions which allows it to remain associated to Europol as a ‘third country’ (and a Member State). The bespoke Brexit reality may prove even more complex.