The United Kingdom and France are finalizing a new deal to slow the flow of illegal migrants across the narrow sea between them.

The "one in, one out" deal was discussed in London on Thursday, at the UK-France Summit, during day three of President Emmanuel Macron's state visit to the UK.

As the summit began, Macron said: "We would like to collectively, together, hand-in-hand, build what will allow us to address the looming challenges."

Macron and UK Prime Minister Keir Starmer hope the deal will discourage people from boarding smugglers' boats in France to claim asylum in the UK because some arriving in the UK that way will be sent back to France each week in return for an identical number of people with genuine claims being sent from France to the UK.

The arrangement could ease the migrant crisis in both countries. It has also become a major issue for the leaders, with tens of thousands of people claiming asylum annually, placing a strain on resources and feeding the rise of the far right.

The crossing is also dangerous and 80 people have died trying to make it in 2024.

Macron said France shares "the same resolve to fight against illegal criminal gangs" running the people-smuggling operations as the UK.

Starmer said: "We all agree that the situation in the (English) Channel cannot go on as it is, so we're bringing new tactics into play and a new intent to tackle illegal migration and break the business model of the criminal gangs."

Macron has also said the UK should remove pull factors drawing migrants to the country, which led a UK government spokesman to say it is "toughening every part of the system to ensure the rules are enforced and respected" and that migrants are not able to work in the UK.

"The British public won't stand for it and neither will this government," he said.

During an engagement at Imperial College London on Wednesday, Macron also said the situation would have been better if the UK had not left the European Union.

"I'm not sure you fixed migration and financial issues post-Brexit much better than with the EU," he said.

Critics have said, with more than 20,000 people having crossed the English Channel illegally during the first six months of 2025, the anticipated 50-person weekly limit may be too small to make a difference, but supporters said it could be increased later.

Christa Rottensteiner, chief of mission for the United Nations' migration agency, said countries should also look at the root causes of the migrant crisis.