Any adult migrant who arrives on a small boat faces return and, under the arrangement, for every one sent back, a legitimate asylum seeker will travel from France to Britain. They will have a family connection to the UK or come from a country with a high rate of successful asylum claims, such as Afghanistan, Iran or Eritrea.
A trial of the scheme — the first agreement since Brexit to enable the return of small boat migrants — will last almost a year, raising questions over how effective a deterrent it will be.
The Home Office has not said what proportion of arrivals or how many individuals will be returned, but it is understood the pilot scheme will deport about 50 migrants per week, about one in 17 of all arrivals if crossings continue at their current rate.
A senior Home Office source said modelling carried out by officials had estimated measures to combat crossings would need to prevent as many as 85 per cent of all attempts in order to destroy the people smugglers’ business model.
A source close to Yvette Cooper, the home secretary, disputed the modelling, saying it was outdated.
“It doesn’t reflect the full range of policies the new government has put in place to tackle this issue — from our work with the French to stop boats leaving in the first place to the massive expansion in law enforcement activity and the significant increase in deportations,” the source said.
They added that Labour planned to make running migrant crossings unaffordable.
The one in, one out deal with France is one of several government policies aimed at realising Sir Keir Starmer’s pledge to “smash the gangs”.
However, migrant crossings have soared to the highest level since the small boats crisis began in 2018. So far this year 25,436 migrants have crossed the Channel, a figure 49 per cent higher than the 17,031 that had arrived by this time last year.
The prime minister hailed the deal with France as an unprecedented scheme that would target the people smugglers’ business model.
Starmer said: “This government has been fixing the foundations of the broken asylum system we inherited and today we send a clear message — if you come here illegally on a small boat you will face being sent back to France.
“This is the product of months of grown-up diplomacy delivering real results for British people as we broker deals no government has been able to achieve and strike at the heart of these vile gangs’ business model.
“The days of gimmicks and broken promises are over — we will restore order to our borders with the seriousness and competence the British people deserve.”
The agreement, announced last month, allows the return to France of adults who arrive on small boats if their asylum claim is inadmissible. The French government has a veto over which migrants Britain sends back.
In exchange, Britain will accept asylum seekers already in France, who can use an online portal to apply for relocation. Britain also has the power to select or block individuals.
Selection will depend on three factors; having relatives in the UK, having one of the nationalities that is most likely to be granted asylum; and being among those most at risk of exploitation by people smugglers.
While the first migrants to be affected will probably be detained this week, they are unlikely to be removed to France until next month because legal processes and appeals are expected to take several weeks.
Cooper said: “For the first time, under this groundbreaking new treaty, people who undertake illegal, dangerous journeys to the UK — putting lives at risk and fuelling organised crime — can be returned to France. In return, we will take people who apply legally with appropriate documentation to be transferred to the UK, subject to clear eligibility criteria and stringent security checks.
“This is an important step towards undermining the business model of the organised crime gangs that are behind these crossings — undermining their claims that those who travel to the UK illegally can’t be returned to France.”
Chris Philp, the shadow home secretary, said the deal would not be a sufficiently powerful deterrent and reiterated the Conservative party’s call to resurrect the Rwanda scheme, scrapped by Labour days after gaining office.
He said: “Returning just 50 illegal immigrants a week, and probably less, will make no difference whatsoever. This amounts to just 6 per cent of illegal arrivals. Allowing 94 per cent to stay in the UK will be no deterrent at all. This is a gimmick which won’t work.
“The Rwanda removals deterrent, under which 100 per cent of illegal arrivals would be removed, was ready to go last summer but Labour cancelled it just days before it was due to start with no proper replacement plan. As a result, this year so far has been the worst ever for illegal immigrants crossing the channel.
“Only removing all illegal immigrants upon arrival will provide the necessary deterrent to stop the crossings. This is the Conservative plan, but Labour is too weak to implement it and as a result they have lost control of our borders.”
