Theresa May to pull Britain out of the EU’s joint foreign policy-making body in 2019
In reality the UK can not operate unilaterally. This is an area where Brexit is thoroughly incoherent, and probably one of the reasons why foreign policy didn’t get talked about too much in the context of the Leave campaign (foreign policy is very Remain). Where it did get discussed, it was backward looking jingoistic bluster (Dunkirk spirit, Britain as buccaneering, defending the sea lanes for this explosion of international trade that is definitely going to happen after we escape the clutches of the EU).
This bluster was to mask the fact that, whatever the other merits of leaving the EU, Brexiters were acting as Putin’s useful idiots when it came to foreign policy. They’ve weakened both NATO and the EU (and NATO chiefs are clear that a strong EU is good for NATO).
The overtures that May is making in future security cooperation is damage limitation. Nothing more. Nations the size of the UK need to act alongside foreign policy allies in order to magnify their power, and this cooperation comes with the trade off of limiting the available policy set (vs unilateralism) in some ways (in other ways, it increases the policy set through magnifying power).