A 29-year-old is among the hundreds of adult asylum-seekers in Britain who lied to officials and posed as children, according to newly released official figures.

Official age assessments carried out by social workers across the country revealed that a staggering number of those claiming to be lone refugee children were far older than they pretended to be.

In some cases they were close to 30 and could have posed a risk to school pupils or foster families had they not been checked.

Migrants arriving from the Jungle camp in Calais (not those who were found to be older by social workers)

The revelation comes after concerns were raised that some of the refugees allowed into Britain from the Jungle camp in Calais were no longer teenagers.

Figures obtained by The Mail on Sunday from 50 local authorities across England show that social workers carried out 2,028 age tests between 2013-14 and 2015-16. Over these three years, almost one in four of the claimants – 465 – were found to be over 18.

Detailed figures provided under the Freedom of Information Act to this newspaper show that the eldest was found to be almost twice as old as he had claimed.

The man, assessed by Hampshire County Council in 2014-15, claimed to be 17 but was ‘assessed as 29’. In Portsmouth last year, a man claimed to be 17 but was assessed as being 26. And in Manchester in 2013-14, a woman said she was 17 but was also found to be 26.

In Hillingdon, West London, a man who said he was just 15 was assessed as being 25 – a full decade older. Another man was found to be 25, in Newcastle, although he claimed he was just 17. Astonishingly, in some areas almost every claimant considered turned out to be aged over 18.

Last night Tory backbench MP David Davies, who led calls for young asylum-seekers to undergo dental X-rays to determine their real age, said: ‘This backs up everything I’ve been saying and I make no apology for saying we need to have medical checks for people who appear to be over 18.

Two refugees arrive in Britain from the Calais jungle camp, amid concerns many 'children' were lying about their age. These people are not those found by authorities as having fabricated their ages

‘The alternative is that men in their late 20s end up being put in foster homes with vulnerable children and in classrooms, with all the risks that entails to children’s welfare.’

Overall, the number of people arriving in Britain and claiming to be lone refugee children has almost tripled in recent years, Home Office figures reveal, from 1,125 in 2012 to 3,253 in 2016.

The Home Office said it had transferred more than 750 lone children from France to the UK since October 2016 and all of them were age-assessed.