Do or die? The UK, the EU, and internal/external security cooperation after Brexit

The European Union (EU) integration project is under attack from a reassertion of national sovereignty following Brexit and the Covid-19 crisis. Our analysis examines the impact that traditional forms of sovereignty and national interests will have on the conduct of EU foreign and security policy post-Brexit. We focus on the Brexit challenge to the EU mode of regulation and diplomacy in internal/external policies in Common Foreign and Security Policy, Common Security and Defence Policy, and Justice and Home Affairs. The article also considers key scenarios for future UK-EU security cooperation to inform analysis of likely policy outcomes for the UK and the EU. The article concludes that the EU will have a greater impact through its laws and regulations on the post-Brexit UK than vice versa and that Brexit is not an immediate threat to the EU's regulatory mode of security governance. The new realities of internal/external security governance in Europe post-Brexit will mean weakened EU–UK security arrangements, which will impact the scope and quality of European security cooperation beyond traditional defence. This is both undesirable and potentially dangerous for European security cooperation and for Europe's position in the wider world.