Differentiation today is a defining feature of the EU legal order. Member States have selectively participated in European policy areas previously exclusive to the nation state through opt-outs and, later, opt-ins. For the United Kingdom (UK) participation in certain measures in the Area of Freedom Security and Justice (AFSJ) is deemed “vital”. This chapter explores the existing opt-outs, specifically in the field of the AFSJ to elaborate possible paths of flexible integration for the future of the UK as a third country after Brexit. The fact is that the EU has already shown considerable flexibility and political willingness to provide pragmatic solutions for differentiation in AFSJ matters. However, it remains to be seen how much of that political willingness filters into the Brexit negotiations on AFSJ measures and that truly ‘bespoke’ arrangements will emerge of a different nature to those that already exist in scattered ‘bits and pieces’. The UK may moreover as a ’stigmatised’ outsider be forced to ‘mimic’ EU rules and regulations in this area in the future without democratic participation in their content nor in ongoing debates on core issues before the Court of Justice.
Keywords: Brexit, UK, EU, differentiation, security cooperation