One in five young men in youth jails is Muslim, an increase of nearly 25 per cent on last year, figures released today show.
The proportion of youth offenders in custody from black and minority ethnic communities also rose three percentage points to 42 per cent in 2010-11, according to the report by the chief inspector of prisons.
Around 17 per cent of the population of England and Wales is non-white, while it is estimated that about 5 per cent of people in the UK are Muslim.
The annual review of children and young people in custody showed that the proportion of males in young offender institutions (YOIs) identifying themselves as Muslim in 2011-12 rose to 21 per cent from 16 per cent the previous year and 13 per cent the year before that.
But the study, published jointly with the Youth Justice Board (YJB), showed the total number of young people in custody fell by 14 per cent last year.
Meanwhile, 30 per cent of the young people surveyed said they had previously been looked after by a local authority.
Mr Hardwick said the figure was "depressingly high".