Getty Child refugees from the Calais Jungle camp were rehomed in the UK

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The young refugees, brought over six weeks ago, have been pursued by traffickers via social media for money they previously agreed to pay to get into the UK before the British Government stepped in. David Simmonds, a spokesman for the local councils caring for the 750 children brought over since October, said he believes they have been forced into prostitution or slavery in sweatshops so they can raise the promised money. A 16-year-old from the Jungle who had been housed in Croydon, south London, went missing and was later found by police working as a prostitute.

Absconding is a big problem, specifically from this cohort David Simmonds, LGA

Mr Simmonds, chairman of the Local Government Association’s asylum, migration and refugee department, said: “Absconding is a big problem, specifically from this cohort. "The traffickers have an online relationship with the refugees. They pick them up on Facebook and subject them to threats. “They say, 'We know where your little brother is, he's still in France’. “We are hearing examples with this cohort who are being pursued, and that is definitely an issue. We have seen examples of where the young people have gone missing."

Getty David Simmonds said social services have no way of keeping young people in a secure environment

A number of local refugee groups said they are aware of six cases where children recently arrived from Calais disappeared from council care. One support worker said: “That will not be the limit of it. It may be the tip of the iceberg.” Lord Dubs amended the Immigration Act in order to legally allow the children to be brought to Britain and said the revelation was “shocking and very disappointing”. He said: “They were brought here to be safe. It is important that local authorities have the resources to look after these children, and give them enough support so they can't be got at by traffickers." The scheme has now been halted.

Some brought over from Calais have been accused of lying about their age but support workers said trafficking gangs have “piggybacked” onto the Government’s operation so they can force them into labour or sex work. They said some are genuinely younger than 18 while others are blackmailed by traffickers to say they are. Mr Simmonds said traffickers are exploiting Border Agency rules which say those claiming to be under 18 should be given benefit of the doubt unless they appear older than 25.

Getty The Calais Jungle camp was demolished in the summer

Getty Lots of the child refugees have been accused of not being children

He said age assessments for several candidates are now happening and he expected about two-thirds to actually be adults. The deputy leader of Hillingdon council in west London, added: “Social services do not have any powers to keep young people in any form of secure environment. "They are free to disappear should they wish to."

Migrant 'children' from 'Jungle Camp' arrive in the UK Wed, October 19, 2016 Migrant 'children' from the 'Jungle Camp' in Calais arrive in the UK to be reunited with relatives. Play slideshow 1 of 26

Britain has been struggling with unaccompanied child asylum seekers going missing for a number of years Charity Expat UK revealed 593 child asylum seekers in care and 167 trafficked children in care went missing in the year to September 2015. Of those 760, 553 were found, rescued or returned themselves but 207 have never been found. Further issues have arisen from the Calais programme, including for children placed with relatives already in the UK.