The first small boat migrants have been detained for removal to France under the new ‘one in, one out’ scheme.
The Home Office confirmed Channel arrivals were held after they were brought into Dover yesterday.
It did not disclose how many migrants had been held.
But the detentions come amid huge concerns that human rights challenges and other legal actions could delay migrants being sent back for months, as well as scepticism over the narrow scope of the scheme.
Migrants selected for removal will be held in Home Office detention facilities rather than being sent to live in taxpayer-funded asylum hotels.
Home Secretary Yvette Cooper said: ‘Yesterday, under the terms of this groundbreaking new treaty, the first group of people to cross the Channel were detained after their arrival at Western Jet Foil [at Dover port] and will now be held in detention until they can be returned to France.
‘That sends a message to every migrant currently thinking of paying organised crime gangs to go to the UK that they will be risking their lives and throwing away their money if they get into a small boat.
‘No-one should be making this illegal and dangerous journey that undermines our border security and lines the pockets of the criminal gangs.’
She added: ‘Criminal gangs have spent seven years embedding themselves along our border and it will take time to unravel them, but these detentions are an important step towards undermining their business model and unravelling the false promises they make.
‘These are the early days for this pilot scheme, and it will develop over time.
‘But we are on track to do what no other government has done since this crisis first started – sending small boat arrivals back to France and strengthening our borders through the Plan for Change.’
As part of the treaty Britain will accept migrants from France in exchange for small boat arrivals.
That element of the scheme also began today, allowing migrants to lodge ‘expressions of interest’ on a specially-created Home Office website.
It comes after a Cabinet minister appeared to contradict the terms of the new treaty with France yesterday.
Culture Secretary Lisa Nandy said small boat migrants sent back under the deal would see their human rights claims heard after being sent back to France.
However, it later emerged that some types of human rights cases would, in fact, block the Home Office from being able to remove migrants in the first place.
The treaty clearly sets out how small boat migrants cannot be sent back to France if they have ‘an outstanding human rights claim’.
The Home Office confirmed some human rights claims will block migrants’ removal until they have been concluded in full.
It will include cases which cannot be formally ‘certified’ by officials as ‘clearly unfounded’.
The Mail has learned pro-migrant groups have begun informal discussions about launching a joint legal action against Labour’s plan – just as they did against the Tories’ Rwanda asylum scheme.
Sources said there had already been ‘a certain amount of co-ordination’ between charities and other groups, with details of the treaty still being analysed.
Meanwhile, the Free Movement website, which offers advice to immigration lawyers, yesterday published an analysis of the new measures which said: ‘Legal challenges will be more difficult than for Rwanda, however there are still likely to be grounds on which some people can resist removal to France.
‘For example, if the inadmissibility decision was wrong, if people have family in the UK, or had experiences in France which make it inappropriate to send them back.’
It means the Home Secretary is likely to face a huge legal battle to get the first migrants removed from Britain.
Last month Prime Minister Sir Keir Starmer pledged migrants would be ‘detained and returned to France in short order’ under the agreement.
But yesterday – the first day it was in force – Shadow Home Secretary Chris Philp posted videos from the Channel as he watched migrant boats bound for the UK coast, escorted by a French vessel.
He said it showed the Anglo-French deal was a failure, adding that occupants of the boats were ‘coming to a hotel near you soon’.