UK Prime Minister Keir Starmer and French President Emmanuel Macron, with senior ministers, during the UK–France Summit at 10 Downing Street in London, part of Macron’s three-day state visit to the UK, 10 July 2025; Credit: Reuters/Gonzalo Fuentes/Pool

NORTHWOOD (Reuters) - France and the UK on Thursday 10 July 2025 agreed to reinforce cooperation over their respective nuclear arsenals as the two European powerhouses seek to respond to growing threats to the continent and uncertainty over their US ally.

The announcement came after French President Emmanuel Macron concluded a three-day state visit to the UK, where the two allies sought to turn the page of years' of turbulence following the UK's decision to withdraw from the European Union.

"This morning, we signed the Northwood declaration, confirming for the first time that we are coordinating our independent nuclear deterrence," British Prime Minister Keir Starmer told a news conference alongside Macron.

"From today, our adversaries will know that any extreme threat to this continent would prompt a response from our two nations. There is no greater demonstration of the importance of this relationship."

US President Donald Trump's questioning of burden-sharing in NATO and his overtures to Russia have led to existential questions in Europe about the trans-Atlantic relationship and Washington's commitment to helping defend its European allies.

Europe's primary nuclear deterrence comes from the United States and is a decades-old symbol of trans-Atlantic solidarity.

Macron said the two countries had created an oversight committee to coordinate their cooperation, a task he said was vital.

"The decision is that we don't exclude the coordination of our respective deterrents. It's a message that our partners and adversaries must hear," Macron said.

The closer cooperation had nothing to do with their efforts to create a coalition of the willing to support Ukraine in the event of a ceasefire with Russia, he added.

While both sides will keep their own decision-making processes and strategic ambiguity, the move does suggest further protection for the continent at a time when the United States' commitment to Europe is under scrutiny.

Macron has previously said he will launch a strategic dialogue on extending the protection offered by France's nuclear arsenal to its European partners.

The US has nuclear arms in Europe and tens of thousands of troops deployed in bases across the continent with military capabilities that Europe cannot match.

France spends about 5.6 billion euros annually on maintaining its stockpile of 290 submarine- and air-launched nuclear weapons, the world's fourth largest.

The UK describes its nuclear programme as "operationally independent", but sources missile technology from the US and depends on the US for acquisition and maintenance support.

"On the nuclear agreement that we've reached today ... it is truly historic," Starmer said.