Over the past decade, the UK and the countries of the EU have experienced very similar, and deeply troubling, security challenges as a result of the military threat from Russia, disengagement and hostility from the US, and the possibility of economic coercion from China. The UK’s 2025 National Security Strategy specifies a clear way forward, indicating a need for what it calls a “rebalancing” of Euro-Atlantic order, involving closer integration, interoperability and defence industrial compatibility between the UK and its allies in Europe. This deeper integration also has value from the perspective of many European countries. The UK brings with it military, industrial and diplomatic abilities that a number of European states seek to enfold within their security arrangements. As well as direct benefits, greater defence and security integration offer a fruitful way for the UK to deepen its relationship with Europe, at a time when trade and regulatory cooperation remain subject to political and bureaucratic constraints. In this period of geopolitical chaos, stronger defence and security collaboration can help make the UK safer, and could also underpin a valuable geopolitical realignment.