Somalis are the largest group, followed by Romanians and Jamaicans, which make up more than 600 of the 2,000 inmates at Feltham Young Offenders Institute in west London.
Sir Andrew Green, chairman of campaign group Migration Watch, said: “Clearly the efforts made to integrate these people from immigrant communities have failed.”
The Prison Service figures, released after a Freedom of Information request, are for offenders aged 10 to 18 who entered the jail from January 2010 to April 2011.
Out of 2,081, some 632 were born overseas. Of those, 63 – one in 10 – were Somalis. Another 48 were Romanians, 41 Jamaicans, 26 from Afghanistan, and 24 from Nigeria.
Also in the prison’s “top 10” foreigners’ list, 21 offenders were from Algeria and the same number from Lithuania. A total of 48 came from Congo, Ireland and Portugal.
Under UK law, overseas nationals sentenced to more than 12 months can be considered for deportation – but not if they are under 17.
Last night, an extraordinary row broke out after the charity Somali Action on Youth Crime claimed that the figures were “biased”.
Director Mustafa Ibrahim said: “Government forms don’t distinguish between Somalis and people from other parts of Africa, so Somalis get blamed for crimes by other people.”
But a Prison Service spokesman denied the claim, insisting that other African prisoners are not classed as Somalis. He said: “Feltham YOI does not classify African prisoners as Somali – this is categorically untrue.
“Prisons have a self-reporting system where arriving prisoners are asked to state their nationality and place of birth.”