A migrant has returned to the UK on a small boat after being removed to France under the "one in, one out" scheme less than a month ago, BBC News understands.

The Guardian newspaper reported that the man claimed to have been been a victim of modern slavery at the hands of smuggling gangs in France.

The Home Office declined to directly confirm the report but said a migrant had been detained and their removal was being sought as soon as possible.

Forty two people who arrived in the UK illegally have been removed so far under the scheme in which the UK agrees to take in asylum seekers who have a case for protection.

The BBC understands the man is an Iranian national, and was initially detained on 6 August and was removed on 19 September, becoming the third person to be sent to France under the scheme. He returned four days ago on 18 October.

The male migrant - who the Guardian has not named - told the newspaper he returned to the UK because he feared for his life in France.

Speaking about his alleged treatments at the hands of smugglers, he said: "They took me like a worthless object, forced me to work, abused me, and threatened me with a gun and told me I would be killed if I made the slightest protest."

Asked about the report, a Home Office spokesperson said: "We will not accept any abuse of our borders, and we will do everything in our power to remove those without the legal right to be here.

"Individuals who are returned under the pilot and subsequently attempt to re-enter the UK illegally will removed."

Maddie Harris, director of Humans for Rights Network, told BBC News her organisation has been in direct contact with the Iranian man.

She said: "From very on early [after his removal] he was experiencing acute fear... as a result of the experience he had at the hands of the smugglers.

"While in France he experienced horrendous treatment at the hands of the people who are organising journeys to the UK."

She said the man returned because he felt he "was not receiving protection in France and feared those individuals may continue with that horrendous treatment".

She also said her organisation had seen cases of others returned under the scheme who have had "compelling" evidence of mistreatment, and who were not able to receive "adequate legal advice" during the "rushed" removal process.

Asked about the "one in, one out" scheme on Wednesday, a Downing Street spokesperson said: "We've been clear about the arrangement with France, that this is the beginning of a landmark scheme which is not in itself a silver bullet".

The scheme, which was announced in July, is intended to deter people from crossing the Channel and encourage migrants to make asylum claims on the continent. Twenty three people have returned to France.

Under the treaty, France agreed to take back migrants who had travelled to the UK by small boat and had their asylum claim rejected.

For each person returned to France, the UK has agreed to accept someone with a case for protection as a refugee who has not attempted to cross the Channel.

On Sunday, the Home Office said 16 people had been removed to France on a single flight, the largest group removal under the scheme yet.

The Iranian man's return to the UK came as small boat arrivals on Wednesday meant that the number of attempts to cross the Channel this year have now exceeded the 36,816 recorded in 2024.

An official figure won't be confirmed until Thursday.

The record number of arrivals for a single year was 45,755 in 2022, and this year's rate is closely tracking that.

Home Office figures show that there were no crossings on six out of the last seven days but that 369 made the journey on 18 October.