"A former prison governor who led an official review into Islamist extremism in prisons has said jails in the UK have become “incubators” of radical behaviour, and repeated calls for the most subversive offenders to be separated from other inmates. Ian Acheson, who led the independent government review of Islamist extremism in prisons and probation in 2016, said the high number of lower-tariff extremist offenders entering squalid, overcrowded jails, combined with a low chance of them receiving treatment for their behaviour, were behind the worsening problem. He called for the “enlightened separation of extremist ideologues” in prison, but acknowledged it was a “controversial” recommendation. Acheson, writing in an essay published by the Tony Blair Institute for Global Change, said: 'In 2018, 41% of convictions for terrorism-related offences were of sentences of four years or less. In particular, these lower-tariff prisoners enter a penal system severely disordered by overcrowding, squalor and insufficient staff. The prospect of them receiving treatment for their offending behaviour in this environment pales beside the pragmatic attraction of safety in religious or ideological groups that provide security, kudos and structure.'"