Under the Dubs amendment, a limited number of unaccompanied minors across Europe are supposed to be brought to the UK and placed in local authority care.
But The Independent has learnt that some youngsters relocated to Britain have been counted towards the capped total despite already having the right to be in the country under family reunification laws.
Ministers have admitted that children who arrive under the Dubs scheme but are then reunited with family members still count towards the final target of 480, saying placing them with relatives was a decision for local authorities, not the Home Office.
Charities and politicians warn that this means the scheme is leaving children and teenagers stranded on the continent when they should be given refuge in the UK, describing it as a “cruel and callous” means of circumventing the amendment.
Safe Passage, which supports child refugees, knows of two children transferred under Dubs who were reunited with a family member in Britain either immediately or shortly after arriving, and therefore would have been eligible to enter the country anyway. The charity said there were likely to be more similar cases.
Meanwhile, thousands of lone minors remain stranded in Europe, scores of who are sleeping rough in northern France. Only around 250 of Dubs places have been filled two years after the amendment was passed.
Shadow home secretary Diane Abbott told The Independent: “This Tory government has betrayed some of the most vulnerable children in the world.
“If we can reunite some children with their relatives in Britain, then we should absolutely do so. But using this as yet another means of circumventing the Dubs amendment is cruel and callous.
“It is a disgrace that the UK continuously fails to meet its legal and moral obligations to child refugees.”
Lord Dubs said the UK’s responsibilities to child refugees under the Dubs scheme were “distinct and separate” from its obligations to reunite families under the Dublin regulation.
“By classifying a child who joins their family as a Dubs transfer, the government is depriving another incredibly vulnerable unaccompanied child the opportunity to gain protection in the UK,” he added.
“I have written to the home secretary seeking reassurances that the government will meet its legal obligations to all lone child refugees.”
Charities working with child refugees in France said delays on family reunion cases meant some children with family ties in the UK were being transferred under Dubs because it was quicker, leaving lone children who should be considered under the scheme vulnerable to exploitation.
Margot Bernard, field coordinator for Safe Passage in France, said: “Getting to Britain via the family reunion route can take a long time, so if a child with family in the UK is also eligible under Dubs they can get across this way and it might be quicker.
“But we know of other children without relatives who are eligible for Dubs but are not being identified. The process takes so long and this leads them to instead try to cross by themselves, putting themselves in danger and at risk of exploitation by people smugglers.”
Last week, a court ruled that the process used to assess 2,000 refugee children during the demolition of the Calais Jungle in 2016 was “unfair and unlawful”, after hundreds of children were not given adequate reasons for the refusal of their applications to join family members in the UK.
Two hundred lone child refugees are estimated to be sleeping rough on the streets of Paris, while scores of unaccompanied children are living without adequate emergency shelter or proper access to drinking water in Calais and Dunkirk, in what the UN recently described as an “inhumane situation”.
The Independent reported last year that youngsters in the region were becoming increasingly prone to exploitation at the hands of smuggling gangs who promise them a free crossing, sometimes in return for “work” upon arrival in the UK.
Beth Gardiner-Smith, of child refugee charity Safe Passage, said: “The UK government capped the Dubs scheme at just 480 places and now it seems even these small number of places are being used for children who could be transferred under another existing legal route.
“There are many vulnerable refugee children in Europe for whom a place under the Dubs scheme would be life-changing but only around 250 of these places have been filled two years after the law was passed.
“If it’s quicker to reunite a child with family through the Dubs route, that place should then be made available again for another child.
“And the government should get on with identifying those eligible children as well as speeding up family reunion so that all eligible children have fast, safe and legal routes to protection.”
The Home Office has been approached for comment.