Britain will pay France nearly half a billion pounds over the next three years to step up efforts to prevent small boats from crossing the Channel, Rishi Sunak has announced.

The Prime Minister praised the “unprecedented” £478 million (541 million euro) package to fund a new detention centre in France and hundreds of extra law enforcement officers on French shores.

Mr Sunak announced the package after holding talks with Emmanuel Macron during a UK-France summit at the Elysee Palace in Paris on Friday.

The French President told Mr Sunak the migration returns agreement that he covets under his pledge to “stop the boats” would have to be negotiated with the European Union rather than Paris.

The major new package comes on top of the more than £300 million the UK has committed to France in the last decade to help tackle unauthorised migration.

It is the first time the UK will contribute to building a detention centre in France to help deal with the numbers of people being trafficked.

It is understood the centre, which is expected to be located in Dunkerque, will be run by French officials with the UK contributing some 30 million euros over three years.

People detained at the site are to be returned to their home country if safe, or if not, the last country they transited through.

France is expected to spend around five times what the UK will under the overall new agreement, it is understood.

Ministers say twice as many unauthorised crossings were stopped last year than in the previous 12 months and hope this will be further boosted by new drones, aircraft and the additional 500 officers to patrol French beaches.

Mr Sunak said: “We don’t need to manage this problem, we need to break it. And today, we have gone further than ever before to put an end to this disgusting trade in human life. Working together, the UK and France will ensure that nobody can exploit our systems with impunity.”

During a joint press conference at the Elysee, they also announced:

– A new deal on civil nuclear co-operation to prevent dependency on despots’ fossil fuels.

– Plans to train Ukrainian marines to help give them a “decisive advantage” against Vladimir Putin’s invading forces.

– A commitment to ease the post-Brexit barriers to school trips between Britain and France.

Whereas Boris Johnson regularly sparred with Mr Macron over Brexit and a submarines deal with the US and Australia, and Liz Truss was unable to say whether she considered him a “friend or foe”, the president has formed a close bond with Mr Sunak.

The pair spoke for an hour in private, having dispensed with their advisers, and Mr Sunak hailed him as a “friend of Britain” and Mr Macron hailed a “new beginning” in Anglo-French relations.

Mr Macron said he wants to have the “best possible relations” with the UK but they need to “fix” the consequences of Brexit.

But one of those issues he cited was the absence of any returns agreement for asylum seekers that cross each other’s borders.

Mr Sunak has not succeeded in brokering one with France, and Mr Macron said it would not be “an agreement between the UK and France, but an agreement between the UK and the EU”.

There have been suggestions that Mr Sunak’s new asylum legislation that may breach the European Convention on Human Rights may cause a fresh rift with the EU.

But Mr Sunak insisted “we will always comply with our international treaty obligations”, adding: “I am convinced that within them that we can do what is necessary to solve this shared problem and stop the boats.”

More than 3,000 people have already made the perilous sea journey this year. Almost 46,000 arrived on the UK’s south coast in 2022 after making the crossing.

That is despite Mr Sunak and Home Secretary Suella Braverman announcing a £63 million package to increase patrol officers by 40% four months ago. That package followed a £55 million deal in 2021.

Amnesty International UK called for the two countries to commit to “providing asylum” for people instead of “heartless anti-refugee measures”.

Steve Valdez-Symonds, the charity’s refugee and migrant rights director, said: “Fortress Britain policies won’t work and people will continue to drown in the Channel if ministers stubbornly refuse to make safe routes available to people seeking asylum – particularly when they have family or other strong connections here.”

Christina Marriott, executive director of strategy and communications at the British Red Cross, said the focus on detention in the latest agreement was “disappointing”.

“They would be ineffective, hugely expensive, and contrary to the international laws our country was once proud to have shaped. But most of all, this legislation would be devastating for the men, women and children in need of our help,” she said.

Earlier this week Mr Sunak faced claims he was effectively imposing an “asylum ban” after announcing legislation that would prevent anyone who makes unauthorised entries into Britain from ever returning.