British Prime Minister Keir Starmer meets President Emmanuel Macron in London on July 10, 2025. (Photo: Xinhua/ VNA)

At a joint press conference with President Macron on Thursday, British Prime Minister Keir Starmer said the two countries have signed the Northwood Declaration, which will allow them to co-ordinate their nuclear deterrents for the first time. Starmer said any "extreme threat to Europe" would prompt a response by both nations.

France and the UK also reached a new "one in, one out" scheme to reduce English Channel crossings. Under the scheme, migrants arriving in Britain via small boats will be "detained and returned to France in short order," Starmer said. In exchange, another group of migrants will be allowed to enter Britain via a safe, legal, and controlled route.

Britain and France will also increase the Combined Joint Expeditionary Force (CJEF) established more than a decade ago from 10,000 to 50,000 troops.

Starmer said Paris will host the new headquarters of a “voluntary coalition” to support Ukraine in the event of a ceasefire agreement, and plans are underway to establish a coordination center in Kyiv in the near future.