There is a strong rationale for close EU-UK cooperation on security and defence after Brexit. Each side should preserve the principle of cooperation in different arrangements for different areas, from policing to foreign policy.
The EU should embrace the UK’s proposal for a treaty on intra-EU security. Because no such treaty will be ready by March 2019, each side should aim for an interim agreement extending existing arrangements until one is in place.
On foreign policy and defence, the UK should not expect a seat at the table in European bodies, including in discussions around possible CSDP operations. Instead, both sides should establish new arrangements that keep them in touch with the other’s thinking. Regular working-level exchanges rather than a treaty are the aim here, such as monthly bilaterals between the British embassy in Brussels and the PSC chair, and UKREP and the EDA chief executive.
All this is achievable but needs clear principles if it is to succeed. These include: a broad understanding of the components of European security; agreement that unique arrangements are required for a unique situation; and a commitment not to treat security like just another element within the Brexit negotiations.