The Home Office is extending a controversial scheme to stop asylum seekers crossing the Channel in small boats, the Guardian has learned.

The UK prime minister, Keir Starmer, and the French president, Emmanuel Macron, signed a deal they hailed as “groundbreaking” last July, known as “one in, one out”.

Under the terms of the deal, one asylum seeker who arrives in the UK in a small boat is forcibly returned to France in exchange for another in France who has not tried to cross the Channel, being brought to the UK legally.

The two leaders agreed that initially the scheme would be a pilot, which was due to end on 11 June. But the two countries have now agreed to extend the scheme until 1 October, according to Home Office sources.

The aim of the scheme is to deter small boat crossings and stop the people-smuggling gangs. Since the deal was signed, thousands of asylum seekers have continued to cross the Channel in small boats and the smugglers have adapted their business model, launching more vessels from Belgium and offering more expensive journeys to the UK in lorries to bypass police on French beaches.

However, the numbers crossing the Channel so far this year have reduced by approximately a third compared with the same period last year, although this is thought to be partly due to the weather. Many windy days in recent months have made crossings too dangerous.

As of 28 April, 605 people have been returned to France and 581 people have come to the UK under the scheme.

Asylum seekers expressed dismay at the news that the scheme is being extended.

One person who was returned to France after arriving in the UK in a small boat said: “I am so sorry to hear this news. It is truly very upsetting. Extending this decision won’t stop refugees from coming. As we’ve seen the small boats are continuing.”

A second asylum seeker who was detained for “one in one out” and was later released to have his asylum claim processed in the UK, said that asylum seekers were suffering both in UK detention centres and after being sent back to France.

They said: “So many people sent back to France have disappeared and nobody knows where they are.

“Many were fingerprinted in Bulgaria, which does not treat asylum seekers well. They have disappeared because they are frightened of being sent back there. One in, one out is very bad but I fear that whatever scheme the UK government comes up with next to stop asylum seekers trying to find safety in the UK will be even worse.”

A Home Office spokesperson said: “Under our returns agreement with France, we have deported more than 600 illegal migrants from British soil. This contributes to the nearly 60,000 illegal migrants who have been returned since July 2024 up 31% on the 19 months prior.

“This is just one part of our wider reforms to remove the incentives that draw illegal migrants to the UK and ramp up the return of those with no right to be here.”