Image caption The cause of the increase in Muslims in youth jails is not known

The proportion of young offenders in England and Wales describing themselves as Muslim has risen.

One in five males in young offender institutions (YOIs) identified themselves as Muslim in 2011/12, compared with 16% in 2010/11.

The director of the Prison Reform Trust, Juliet Lyon, said it was "a big increase" but the reasons were unclear.

The proportion of youths in custody from black and minority ethnic communities also rose from 39% to 42%.

Ms Lyon said: "It could simply be there are more young Muslim men at the moment in the general population than there were a couple of years ago, but equally - and I think it's important that the Prison Service investigates this - it could be that more young people are going to prison and then either converting to the Muslim faith whilst they're in prison or they're reverting to the Muslim faith."

The study, published jointly by the chief inspector of prisons, Nick Hardwick, and the Youth Justice Board (YJB), showed the total number of people aged 15-18 in custody fell from 1,822 in 2010/11 to 1,543 in 2011/12.

The figures are perhaps surprising considering the 2011/12 year included the riots in London and elsewhere in August 2011.

Amjad Malik QC, president of the Association of Muslim Lawyers, said the survey involved "self-description" and it was wrong to think that one in five young males in custody were "practising Muslims".

He told BBC Radio Five Live: "You can't commit crimes and describe yourself as a practising religious person."

Drugs menace

Mr Malik said the young Muslim offenders might come from black or south Asian communities which have poor "life chances" and he added: "I have seen over the last 15 to 20 years a massive volume of drug offences up and down this country. It's a terrible disease. It's the crime of choice because of the economic results, because of the money that can be made from drugs."

Other figures from the chief inspector of prisons' annual review of children and young people in custody, found a quarter of young men in custody said they had been bullied or attacked by a fellow inmate and 23% claimed to have been "victimised" by a prison officer.

And the proportion number of young people in custody who had grown up in the care system - 30% - remained "depressingly high", said the report.