“Lax” Home Office rules were said to be letting in “hulking young men” instead of those genuinely in need of sanctuary.
Officials yesterday admitted the arrivals are being given asylum without any proper medical checks on their age because they are considered “intrusive”.
As more arrived in Britain yesterday, the Home Office said they are given the “benefit of the doubt” if their age is in question.
Tory MP David Davies said: “They are giving hospitality to hulking young men. I think we have been taken for a ride once again.”
Giving migrants the benefit of the doubt was “wrong”, said the MP for Monmouth, adding: “It is absolutely certain some people do lie about their age. We should start from the principle people will do or say anything to get into the UK.”
Britain is allowing in children from the Calais Jungle before it is demolished by the French.
The first 14 arrived on Monday and it is thought as many as 400 could end up being given a new home in the UK.
The “children” who have been allowed in from northern France were joining relatives already in Britain, the Home Office said.
It insisted all had undergone rigorous interviews and checks on documents to try to prove they were under 18.
Their appearance is also used to see if migrants look as young as they claim. But they are only rejected if they are clearly over 18.
Extensive medical tests, including examining dental records, have been ruled out as too “intrusive”.
Home Office guidance on age assessment says: “Applicants whose age has not been accepted by the agency will initially be afforded the benefit of the doubt and be treated as children.”
A spokesman said: “The priority in this process is to safeguard the children and reunite them with families in the UK.”
Immigration rules state asylum claims must be made in the first safe country a person reaches.
But children can have their application transferred to another country if they have family ties there.
Yesterday the Daily Express twice asked the Home Office whether it receives “credible and clear documentary evidence” to prove child migrants’ claimed ages.
A spokesman said the department “would not comment on specific cases” and said the total number of children allowed in would only be revealed once all had arrived.
Mr Davies added: “I worry that just by accepting their word we are putting other people at risk. The UK has set a very dangerous precedent. Anyone in their 20s or 30s can head to Calais, say they are 15 and claim to have relatives in the UK. It is almost certain some are economic migrants.”
Even volunteers working in the Jungle camp said the vetting process is so shambolic vulnerable children are being left behind in the chaos.
One said: “It is a complete mess. Those at the front of the queue are not the most needy and vulnerable – they are the adults pretending to be children.”
Daily Express columnist and former shadow home secretary Ann Widdecombe said: “The process is extremely lax and it always has been. Common sense would say a lot of them are not kids.”
The Home Office went on to explain: “All individuals are referred to the UK authorities by the France terre d’asile (FTDA) and then interviewed by French and UK officials. Where credible and clear documentary evidence of age is not available, criteria including physical appearance and demeanour are used as part of the interview process to assess age.”
• A man was found dead in the back of a lorry yesterday on the A20 in Sellindge, Kent, after suffocating during the journey from Calais.