An MP has called for dental checks on refugees who claim to be children.

The Conservative member for Monmouth, David Davies, said some teenagers photographed arriving in the UK on Monday under a scheme to resettle unaccompanied minors “don’t look like children”.

He called for claimants to have their teeth or wrist bones X-rayed to check their real age, denying that such tests would be “intrusive”.

Mr Davies was later accused of “disgraceful xenophobic rhetoric” by an SNP MP, but defended himself by saying: “I don’t want to vilify anyone, and I would like to see genuine children being brought in, but I think we have got a right to raise this question.”

It’s obviously an emotive subject. What are the facts?

Who are these young refugees?

The 14 young people photographed arriving this week are the first of several hundred unaccompanied children now living in refugee camps on the outskirts of Calais, whom Britain has agreed to take in.

There are an estimated 1,000 such young asylum seekers in the notorious camps. The French government is about to close them down and disperse the people living there.

The UK government has agreed to resettle children who are judged to have direct family connections to this country.

It’s not yet clear what the final number will be but the home secretary, Amber Rudd, said campaigners had identified 387 children as having a legal case for coming to Britain, and the French authorities had agreed to check their identities.

Does the Home Office check their ages?

The Home Office said the 14 teenagers who arrived this week had already been interviewed by French and British officials, who were satisfied they were genuine child refugees.

A Home Office spokesman said: “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.”

The full details of this joint checking process has not been made public.

Ordinarily, British asylum officials treat applicants who claim to be children as adults if they have no documents proving their age and “their physical appearance/demeanour very strongly suggests that they are significantly over 18 years of age”.

The decision has to be signed off by a supervisor and can be overturned if new evidence of age comes to light. All other young people who cannot prove their age are given the benefit of the doubt.

But young asylum seekers can be subject to something called a “Merton test” later if the local authority tasked with looking after them doubts their age.

Council social workers carry out detailed interviews to try to piece together the claimant’s background and likely age, but are not supposed to make a decision based on appearance alone.

Is the Home Office going to start doing dental tests?

No. A spokesman said: “We do not use dental X-rays to confirm the ages of those seeking asylum in the UK. The British Dental Association has described them as inaccurate, inappropriate and unethical.”

Both the last Labour government and the Conservative-Liberal Democrat coalition made noises about introducing dental tests, only to quietly drop the plans.

Some local authorities have reportedly tried to use dental age tests rather than stick to the Merton guidelines.

How accurate are dental tests?

There appears to be a difference of expert opinion about this, but everyone agrees that dental imaging is not completely accurate as a judge of age.

Tim Cole, professor of medical statistics at UCL, told FactCheck that dental imaging used to test whether someone was over 18 or not would give the wrong result about one third of the time.

And that “error rate goes up slightly” when you start testing people of different racial and ethnic groups, he added, since people of different races mature at slightly different rates.

Professor Graham Roberts, a paediatric dentist at King’s College London, has disputed that dental age assessment is harmful or unethical, writing that it “is not precise but it provides a realistic quantifiable estimate of age which is not matched by any other method”.

Comparison of dental tests with genuine birth certificates shows that “42 per cent of the age estimates are within six months of the true age and 68 per cent of age estimates are within one year of the true age” he wrote in an article in the British Dental Journal.

What are the ethical problems?

The British Dental Association – the main trade union and professional body for dentists –  says: “It is inappropriate and unethical to take radiographs of people when there is no health benefit for them.

“X-rays taken for a clinically-justified reason must not be used for another purpose without the patient’s informed consent, without coercion and in full knowledge of how the radiograph will be used and by whom.”

The Refugee Council says it has heard of cases of young people told they will be treated as an adult claimant unless they consent to a dental x-ray, or told that the X-ray results can accurately determine a young person’s age – which isn’t true.

“We became aware of this practice after young people we were helping were to be sent for X-rays without informed consent being gained,” the campaign group said.

Other individuals and organisations who have objected to dental X-rays on ethical grounds in the past include the General Dental Council, the Royal College of Paediatrics, Children’s Commissioners and Chief Medical Officers.

Is there a better way of assessing age?

Not that we know of.

Britain used to X-ray claimants’ wrist bones to try to assess their age, but the practice has been widely discredited.

The Conservative Home Secretary Willie Whitelaw banned bone X-rays in 1982 after hearing expert evidence that it was “unlikely to provide more accurate evidence of age than the assessment of other physical characteristics of an individual”.

In 2011 the Australian authorities were forced to free a number of young Indonesian fishermen they wrongly jailed as adults for people smuggling.

Bone X-rays had been used to decided the defendants’ ages, but Australia has now agreed not to use the method.

Other countries in Europe use a range of methods, some of them controversial.

Many do carry out bone and dental X-rays – despite scepticism from doctors – and genital examinations have been reported to have taken place in Austria and Germany, although the practice was recently banned in Germany.

How many adult asylum seekers pretend to be children?

A lot of news stories say things like: “Two-thirds of child refugees screened by the Home Office to the year September 2015 were later found to be adults.”

That doesn’t mean two-thirds of all people who claim to be child refugees are lying.

The latest figures we have from the Home Office cover the year to June 2016. In those 12 months, There were 3,472 asylum claims from unaccompanied children.

Officials were suspicious about less than a third of those claimants, and 933 age disputes were resolved. Of those cases, 636 were ruled to be over 18.

So about 18 per cent of all people who say they are unaccompanied children ended up being treated as adults. It’s hard to say they were “proved” to be over 18, since in most cases there will be no definitive proof of age.

And there is another side to this story: genuine children being wrongly treated as adults on the basis of their appearance.

We can’t say for sure how often this happens, but the Refugee Council says it regularly takes on cases of young people being wrongly treated as adults and held in detention.

The organisation says it has supported 41 young asylum seekers whose age was disputed since October 1 2014. Of those, 20 have been reassessed and found to be children, and most of the others have been released from detention pending an assessment.