Starmer and Macron Agree to Nuclear Deterrence Pact to Fend Off Threat to Europe

Prime Minister Keir Starmer of Britain and President Emmanuel Macron of France will announce on Thursday the details of a new defense relationship that will include a first-ever pledge to have their nuclear arsenals work together in the event of serious danger to allies in Europe.

The announcement will come as the two leaders conclude a three-day state visit with a trip to a British military base as they seek to underscore their support for defending Ukraine against Russian aggression.

The agreement between the two countries will affirm that “there is no extreme threat to Europe that would not prompt a response by both nations,” according to a statement published late on Wednesday by the British Ministry of Defense.

The announcement expected on Thursday is not a full guarantee of nuclear protection for European nations, but experts said it is a small step in that direction.

Mr. Starmer and Mr. Macron, who last held a similar summit before President Trump’s return to power in January, are also expected to announce some kind of migration agreement that could reduce the number of people attempting to cross the English Channel in small, crowded boats launched from the beaches of northern France.

Both topics are at the core of what the two leaders say is an improved diplomatic relationship between the neighbors that was frayed when British citizens voted, by a narrow majority, to leave the European Union in 2016.