Child refugees sent from the demolished Calais “jungle” to supposedly safe welcome centres across France claim they have been pressed into forced labour.

Legal interviews with unaccompanied minors dispersed from the refugee camp to France’s official reception centres have uncovered allegations that children have been forced into unpaid work and ordered on to farms to pick apples for French supermarkets. Youngsters said they were too scared to refuse the work because they feared it would harm their chances of claiming asylum to the UK.

Of 33 teenage boys interviewed by the charity Safe Passage UK, a quarter also said they had not been given clean clothes since they arrived at the centres after the demolition of the notorious Calais camp nearly four weeks ago.

Offering a glimpse of the conditions inside some of the 60 or so refugee accommodation blocks set up by French authorities, 39% of the minors interviewed said they felt better off in the Calais camp, a site routinely described as a slum unfit for human habitation.

One of the teenage boys, based in a camp in northern France, said: “It is horrible. We worked all day picking apples and were left to eat the rotten ones. The rest went to be sold in France. We just want to be with our family in the UK.”

Another said they were each forced to pick 4kg of fruit every weekday afternoon, while staying at a French reception centre, and worked under the fear that refusing to do so would impair the chances of making it to the UK. He said: “We are scared not to do it in case it affects our asylum claims. What if they don’t let me live here and kick me out?”

In July, Theresa May vowed to make it a priority to rid the world of the “barbaric evil” of modern slavery, and said the forced labour of minors was one of its ugliest manifestations. On WednesdayHome Office minister Robert Goodwill told MPs that children in the welcome centres were “in a place of safety and being well looked after” and he had “not received any concerns about the facilities”.

Facebook Twitter Pinterest The Calais ‘jungle’ was demolished nearly four weeks ago. Photograph: Pascal Rossignol/Reuters

Rabbi Janet Darley, a spokeswoman for grassroots community group Citizens UK, which includes Safe Passage UK, said: “We are hugely concerned about the safeguarding of children in France. Our team have had reports of forced labour, and unaccompanied children being required to live with adults.”

Safe Passage UK interviewed each child for 45 minutes in their own language last week: five children revealed they did not feel safe; of the 33, only five said Home Office officials had spoken to them, with three saying they had not yet been interviewed by any official, from either France or the UK; and three said adults were living with them in their accommodation, raising child protection issues. One said: “It looks like a prison. We don’t have any things to play, and all the time we are staying in our room and it is not safe for us. We live in the middle of adults, their ages are over 20 years.”

Another added: “I am not happy staying in this accommodation, please, please take us out of here to the UK. We have no proper food, clothes and I am bored here. If the situation continues like this, I may go somewhere else.”

The UK charity said two boys it had been in contact with had absconded and another two were considering running away, if their situation did not improve. “If others run away I am not going to stay,” said one child.

Bishop Paul Butler, another spokesman for Citizens UK, said: “Children in France are getting increasingly desperate as they hear little from officials, and fill the void with rumours and speculation.”

So far, about 350 children have been transferred to the UK, with the Home Office expecting several hundred more to be transferred from France under both the Dubs amendment and the Dublin regulations. However, charities say around 2,000 unaccompanied minors were registered in Calais before the demolition and they are campaigning for 1,000 to be brought over before Christmas, after home secretary Amber Rudd said the UK would take “half” last month.

The Home Office said it “remains absolutely committed to bringing all eligible children to the UK as soon as possible” and that children in the welcome centres are being assessed to see if they are eligible under the Dubs amendment. The Home Office’s new guidelines last week stipulate that only unaccompanied teenagers from Syria and Sudan are eligible to enter Britain from France, a decision condemned by charities.