According to government figures there are more black, Asian and minority ethnic youths in young offender institutions and secure units than white people for the first time.
The announcement comes as a Labour MP said that jurors favoured white, middle-class defendants.
Ministry of Justice figures show that in May there were 415 black, Asian and minority young people in custody in England and Wales compared with 396 white young people, or 51 per cent to 48 per cent, with 1 per cent “not known”.
It was the first time the monthly youth custody figures had shown a higher number of black and minority ethnic under-18s than whites in young offender institutions, secure training centres and secure children’s homes.
The 2011 census from the Office for National Statistics showed that 20 per cent of the under-18s in Britain were not white.
Pippa Goodfellow, director of the Standing Committee for Youth Justice, said: “The latest youth custody statistics are a cause of great concern, as they demonstrate the sheer extent to which the criminal justice system is disproportionately propelling black and minority ethnic children into prison.”
In the past ten years the number of under-18s in custody has fallen from about 2,900 to just over 800 in May as part of a government policy to reduce numbers by diverting youngsters away from the formal justice system.
However, the figures show the proportion of whites in custody has fallen at a greater rate than for black and minority ethnic young people.