The “unprecedented” package will help fund a new detention centre near Dunkirk, more drones and an extra 500 police officers to prevent migrants making the dangerous journey across the English Channel.
But critics questioned how this agreement would work when others in the past have had limited success.
More than 40,000 migrants arrived in the UK on small boats last year and the home secretary Suella Braverman has suggested this year’s figure could be twice that.
The announcement came as Mr Sunak travelled to Paris for a summit with Emmanuel Macron, who is viewed as crucial to resetting Britain’s relations with the wider European Union.
Announcing the new package, the PM described their meeting as “a new beginning – an entente renewed,” adding that the pair were “writing a new chapter in this relationship”.
Mr Macron echoed the sentiment, calling the summit “a moment of reunion, of reconnection and of a new beginning”.
But despite the upbeat mood, Mr Macron outright rejected the idea of a deal where France would take back those who travel to the UK on small boats.
Britain has already committed more than £300m to France in the last decade to help tackle unauthorised migration. It will now contribute €141m (£125m) in 2023-24, €191m in 2024-25 and €209m in 2025-6. The French will spend significantly more, understood to be between three and five times as much.
A previous agreement with France designed to prevent crossings was revised in November to be worth around £63m in 2022-23, £8m more than the previous year.
It is unclear how many people will be held in the detention centre in the Dunkirk area. It will be based on existing facilities elsewhere in France and detain those found to be illegal immigrants, who will then be returned to either their own country or a separate safe country.
The centre is designed to deal with those who try persistently to cross the Channel. French officials already seize vessels and prosecute criminal gangs but it is not an offence in France to set off in a small boat.
Tory MPs last night said the huge sums had to deliver value.
Dover MP Natalie Elphicke said: “The French summit small boats deal is an eye-watering financial commitment from the UK, that now needs to be met by equally determined French action to actually stop the boats leaving.”
Former cabinet minister Robert Buckland said the announcement was “big money”, adding: “You’d want to see a correlation between that spend and results on the ground.”
Shadow home secretary Yvette Cooper said: “Rishi Sunak has failed to secure a strong enough agreement with France to deal with the dangerous boat crossings. He has failed to get a returns agreement in place and it looks like his planned new law will make it even harder to get that vital agreement with Europe. Meanwhile, some of the border cooperation measures won’t even be in place for several years even though the problem is now.”
Alistair Carmichael, the Liberal Democrat home affairs spokesperson, said: “Time and again, this government has signed deals with France to stop these Channel crossings – and time and again, they haven’t worked.”
France says migrants can only be detained if they are under a legal obligation to leave France, have been banned from the country, or are subject to a deportation order. They can be held for a maximum of 90 days before they must be deported or released.
An immigration detention centre is already open in Coquelles, near the Channel Tunnel entrance and only around 30 miles from Dunkirk.
Clare Moseley, founder of the Care4Calais charity, said the site is used to “hold people for up to three months for deterrence”.
“This has been happening since 1999 but they still think ‘let’s try it again’, it’s insane,” she told The Independent. “They’re running out of things to give France money for, there isn’t a bit of Calais left that you can put fences up in, they’ve done the drones, so it’s like: ‘Here’s another headline-grabbing announcement.’”
Mr Macron said the sums involved were “commensurate” with the current need. He added that while working together on the ‘small boats’ issues, Britain and France had “dismantled” 55 organised crime networks.
Mr Sunak said giving France money was a “sensible investment” when the UK is spending more than £5m a day on temporary accommodation for migrants, including hotels.
Charities criticised the deal as “anti-refugee”.
Amnesty International UK called for the two countries to commit to “providing asylum” 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.
“Throwing more money at the French, the Rwandan or any other government cannot fix what the UK government has wrecked.”
Christina Marriott, executive director of strategy and communications at the British Red Cross, said the focus on detention was “disappointing”.
In a sign of how much Anglo-French relations have thawed, the two leaders abandoned tradition and held a one-to-one meeting with no officials present for more than an hour.
Relations with France, which proved frosty during Boris Johnson’s tenure, reached a new low last year when ex-PM Liz Truss said the jury was “out” on whether Mr Macron was a friend or a foe.
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