The UK has detained the first small-boat migrants under a “one in, one out” returns treaty with France, as pressure grows on Prime Minister Keir Starmer to stem the influx of asylum-seekers across the English Channel.

Britain said it will begin implementing a deal to return some migrants who arrive on small boats to France within days, a key part of its plans to cut illegal migration, after a treaty on the arrangement is ratified on Tuesday.

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 and will now be held in detention until they can be returned to France.