Britain and France have publicly committed for the first time to coordinating their independent nuclear deterrents in response to extreme threats, signalling a new phase in bilateral and NATO nuclear strategy.

The joint declaration, signed during President Emmanuel Macron’s state visit to London, affirms that the UK and France maintain sovereign nuclear arsenals but are now prepared to align them in the event of a major crisis. It states unequivocally that “any extreme threat to Europe would prompt a response by both nations.”

This is the most explicit public statement yet of the two countries’ willingness to coordinate nuclear posture and response. Until now, both have emphasised independence as the foundation of credible deterrence. The change reflects growing concern about Russia’s nuclear rhetoric and wider instability in the Euro-Atlantic region.

Prime Minister Keir Starmer hailed the agreement as a milestone in European defence. “As close partners and NATO allies, the UK and France have a deep history of defence collaboration and today’s agreements take our partnership to the next level,” he said. “We stand ready to use our shared might to advance joint capabilities while keeping our people safe.”

The UK and France are Europe’s only nuclear-armed powers and two of NATO’s three nuclear states, alongside the United States. Though both nations contribute separately to the alliance’s deterrent posture, this declaration goes further, raising the prospect of integrated decision-making in scenarios involving existential threats.

Defence Secretary John Healey said the new posture underlines shared resolve. “This partnership strengthens our leadership in Europe and sends a clear signal to our adversaries that we stand stronger, together,” he said.

The declaration is part of a broader update to the Lancaster House treaties, including a reinforced Combined Joint Force with cyber and space capabilities, and closer integration across strategic planning. Officials say it reflects a maturing of UK–France defence cooperation after years of joint deployments, industrial collaboration, and shared nuclear research.

By formalising coordination at the highest level of deterrence, London and Paris are aiming to deter adversaries through a united nuclear front, while also demonstrating European strategic autonomy within NATO’s framework.

Britain and France have agreed to co-ordinate their use of nuclear weapons for the first time to defend Europe from “extreme” threats.

In a declaration signed during Emmanuel Macron’s state visit to the UK, the French president and Sir Keir Starmer pledged to work “more closely than ever before” on nuclear deterrence.

With the threat from Russia growing, the agreement opens the door to Europe’s two nuclear powers co-ordinating their deployment of nuclear-armed submarines and fighter jets during a crisis.

In recent months, Germany has called on France to more explicitly commit itself to defending the rest of Europe amid concerns that Donald Trump is poised to scale back the US military’s presence on the Continent.

France is part of Nato but has traditionally maintained a completely independent nuclear posture, while Britain’s deterrent forms a key part of the alliance’s defence strategy.

The new UK-France declaration suggests Paris will soften that position to collaborate with London on planning. It says the nuclear arsenals of both countries “remain independent but can be co-ordinated and that there is no extreme threat to Europe that would not prompt a response by both nations”.

On Wednesday, the Ministry of Defence said this meant “any adversary threatening the vital interests of Britain or France could be confronted by the strength of the nuclear forces of both nations”.

This flimsy vessel carrying migrants could reach British waters in a few hours’ time

By Adam Parsons, Europe correspondent in the English Channel

We see the boat from a distance – the orange of the life jackets reflected in the rising sun.

And as we draw closer, we can make out dozens of people crowded on board as it sets off from the shore, from a beach near Dunkirk.

There is no sign of any police activity on the shore, and there are no police vessels in the water.

Instead, the migrants crammed into an inflatable dinghy are being watched by us, on board a private boat, and the looming figure of the Minck, a French search and rescue ship that soon arrives.

The dinghy meanders. It’s not heading towards Britain but rather hugging the coast.

A few of the passengers wave at us cheerfully, but then the boat starts to head back towards the shore.

Watch: Small boat crammed with migrants in Channel

As it nears a different beach, we see a police vehicle – a dune buggy – heading down to meet it.

Normal practice is for French police officers to slice through the material of any of these small boats that end up back on shore.

Two police officers get out of the buggy and wait. A police helicopter arrives and circles above, performing a tight circle over the heads of the migrants.

The police think they might be about to go back on to the beach; in fact, these passengers know that most of them are staying put.

The boat stops a short distance from the shore and four people jump out. As they wade towards the beach, the boat turns and starts to head back out to sea.

Watch: Why do migrants want to come to the UK?

We see the two police officers approach these four men and have a brief conversation.

They don’t appear to check the bags they are carrying and, if they do question them about why they left the boat, it is the most cursory of conversations.

In reality, these people probably don’t speak French but they were almost certainly involved in arranging this crossing, which is against the law. But all four walk away, disappearing into the dunes at the back of the beach.

We follow the boat as it chugs off in the direction of Britain, carrying around 50 people.

The Minck returns to shadowing its progress, but its job is limited to offering help if the boat gets into trouble.

Otherwise, if the engine keeps working, then this flimsy vessel will reach British waters in a few hours’ time.