“We are working hand-in-hand with our European allies to build a safer, more secure, and more prosperous Europe,” Lammy said.

But a lot can still go wrong, not least because Starmer is under increased pressure following big wins by Reform UK leader Nigel Farage in local elections last week. Farage was one of the most vocal supporters of Brexit and is railing against any government attempt to push the U.K. back into the European fold.

With uncertainty hovering over the future of the NATO alliance under Trump, and Washington threatening to walk away from difficult ceasefire negotiations with Russia and Ukraine, European officials want to land a security deal with the U.K., an allied nuclear power that has a seat on the United Nations Security Council. 

In Paris, however, the urgency to lock arms with the British is tempered by a desire to use the moment to address the bad blood left over from Brexit.

The French are keen in principle on a security alliance with the U.K., but are worried that a bigger deal leaves them open to being blindsided later on more controversial issues, such as access to British waters for EU trawlers.

Under the Trade and Cooperation Agreement with the EU, signed in 2020, European fleets have certain fishing rights and quotas in British waters, but those expire in 2026. France, Denmark and the Netherlands want that access extended.