An asylum seeker who had his private parts measured in a bid to establish his age - at the cost of the taxpayer - has won a key victory in his bid to be declared a child.

The Kurdish teenager, who arrived in the UK from Iraq in the back of a lorry in February this year and can only be named as A, insists that he is just 16 and was born in November 1992.

However the London Borough of Croydon, the local authority in whose care he is, say he is 18.

The boy’s age is crucial, because if he is 16 he will be entitled to welfare payments because he is a vulnerable child.

It could also have an impact on his claim for asylum.

During a judicial review challenge against a Croydon Council ruling that he is 18, lawyers for the legally-aided youngster said that medical evidence supports his claim that he is 16.

And barrister Christopher Buttler, for A, said the local authority were wrong to ignore a medical report filed on his behalf by an experienced paediatrician, Diana Birch.

In June this year, the expert said that A was around 15-and-a-half years, basing her conclusions on his sexual, physical and mental development, his physical growth and his teeth.

Among the factors which Dr Birch took into account was how hairy A is, how deep his voice is - and the size of his genitalia.

However, in October 2008, Croydon ruled that A was 17 - meaning that they believe he turned 18 earlier this month - and rejected Dr Birch's findings Today, at London's High Court, Judge Stephen Morris QC said Croydon had acted "unreasonably" in coming to the conclusion it did.

"The reasons given by the local authority were unsound", said Judge Morris, who said its rejection of Dr Birch's report was "irrational".

"Had Croydon given proper consideration to Dr Birch's report, the outcome of the decision may well have been different," added the judge.

Judge Morris added that Croydon had relied on a March assessment of A, but the reasoning in that report was "relatively superficial" and its conclusion "vague".

Granting the application for judicial review, Judge Morris said Croydon should now reconsider A's claim to be a vulnerable child.