The UK will begin returning migrants arriving in small boats to France within weeks under a new pilot scheme, Sir Keir Starmer has said.

Under the “one in, one out” deal, some arrivals would be returned to France and in exchange the UK would accept an equivalent number of asylum seekers, subject to security checks.

Speaking alongside French President Emmanuel Macron at the end of a three-day state visit, the prime minister said the plan would show that attempts to cross the Channel in small boats would “be in vain”.

It had been reported that the scheme would see up to 50 people a week being returned, but Sir Keir did not confirm any figures.

He said the “ground-breaking” plan would help “break the model” of the people smugglers, and would be ramped up if it was successful.

Illegal migration was, he said, “a global crisis, an EU crisis and a crisis for our two nations”.

Since 2018, when figures began to be gathered, more than 170,000 people have arrived in the UK in small boats. Numbers this year have reached record levels with nearly 20,000 arriving in the first six months of 2025.

Macron said the scheme would have a “deterrent effect” beyond the numbers returned.

He added that Brexit had made it harder for the UK to tackle illegal migration, arguing that the British people were “sold a lie… which is that the problem was Europe”.

During the press conference, the two leaders also announced that their countries would:

• co-ordinate their nuclear deterrents, meaning they would jointly mobilise their weapons in the event of an attack
• strengthen collaboration on supercomputers and AI
• “speed up and accelerate” co-operation on anti-ship missiles.

Some details of the small boats deal, including how the UK would decide who to send back to France, remain unclear, although it is understood the pilot will start with adults.

Those living in France but wanting to come to the UK would be able to express interest in applying for asylum via an online platform.

Priority would be given to those from countries most prone to people smugglers, as well as to people with links to the UK.

In a statement released after the press conference, the government said the agreement would be signed “subject to completing prior legal scrutiny in full transparency and understanding with the [European] Commission and EU Member states”.

Other EU countries – such as Spain and Italy – may have concerns that returned migrants could then be sent to them. Under EU rules, individuals sent back to France would have to claim asylum in the first European country they arrived in, often places bordering the Mediterranean Sea.

Sir Keir said there was “no silver bullet here, but with a united effort, new tactics and a new level of intent, we can finally turn the tables”.

In addition to the returns pilot, he also promised “a crackdown” on illegal working, which would ensure the jobs promised by traffickers to migrants “would no longer exist”.

The government has said it has plans to bear down on illegal working hot spots, such as deliver riders.

Macron said the two countries would “intensify joint action” in the countries of origin and transit.

Announcing the pilot, Sir Keir said: “I know some people will still ask, why should we take anyone in – so let me address that directly.

“We accept genuine asylum seekers because it is right that we offer a haven to those in most dire need.

“But there is also something else, something more practical which is that we simply cannot solve a challenge like stopping the boats by acting alone and telling our allies that we won’t play ball.”

Conservative shadow home secretary Chris Philp said the deal would “only return one in every 17 illegal immigrants arriving”.

“Allowing 94% of illegal immigrants to stay will make no difference whatsoever and have no deterrent effect.”

Reform UK leader Nigel Farage said the crossings were “a national security emergency”.

“Frankly the French owe us our money back,” he added, in a reference to payments made by the UK to support French policing efforts.

He said he did not believe the pilot would work, saying: “If we even try to deport people across the Channel, we will run straight into the European Convention on Human Rights.”

John Vine, a former chief inspector of immigration and borders, told the BBC’s Newsnight programme that establishing the principle that France should take back some illegal migrants was “a first” and “an achievement in itself”.

However, he said the plan would not reduce crossings unless the numbers being returned were “considerable”.

Imran Hussain from the Refugee Council said it was “right” for the government to look at ways of targeting the smugglers’ business model and the proposal would also provide “a mechanism potentially where families have a safe and legal route to come to the UK from France”.

However, the charity Asylum Matters said: “We don’t need another expensive, ineffective, dangerous Rwanda-style gimmick.

“It’s incredibly simple: the only way to stop people from making dangerous journeys is to give them real safe routes to seek sanctuary.”

Labour and the previous Conservative governments have both struggled to stem the numbers coming to the UK in small boats.

The Conservatives had proposed sending arrivals to Rwanda, but the scheme was delayed by legal challenges. The general election was called before it could be implemented.

One of Sir Keir’s first acts as prime minister was to scrap the plan, calling it a gimmick.

He said his government would focus instead on tackling the smuggling gangs that organise the crossings.