There is a "significant risk" of Islamic radicalisation behind bars the head of the prison and probation service has told BBC Panorama.
Michael Spurr the chief executive of the National Offender Management Service of England and Wales (NOMS) told the programme:
"There is a significant risk, given the fact that we manage some very dangerous people.
"Our job is to minimise that risk becoming a reality - that somebody in prison becomes radicalised and commits a terrorist offence."
Over the last ten years the number of Muslims in prisons in England and Wales has doubled, with the figure reaching 11,729 in 2013.
There are about 100 al-Qaida-inspired Islamist terrorists behind bars.
More top news
Drinking three to five cups of coffee a day could reduce the risk of clogged arteries and thus heart attacks, a study has found.
There are five million British expats across the globe. Many have a vested interest in May's election and many still have the right to vote.
Abba's Bjorn Ulvaeus has a boyish enthusiasm for the cashless society - and he has a challenge for ITV News viewers.