Convicted terrorists are to be moved to a “jihadist prison block” to reduce the risk of other inmates being radicalised.
The wing at the Category A Frankland prison in Co Durham will be the first of its kind to open “a prison within a prison” to isolate extremists.
A growing number of criminals are feared to be leaving jails with extremist views. Khalid Masood, the Westminster attacker, is believed to have had “an abrupt religious conversion” to Islam while in Lewes prison, East Sussex. He killed four people in London last week before being shot dead by police.
A government report recommended that the “most subversive extremist prisoners” should be jailed separately to tackle the problem of jihadists radicalising their fellow inmates.
However, Steve Gillan, general secretary of the Prison Officers Association, said that the union was sceptical of segregating such inmates, fearing that it could give them elevated status.
“We have vast experience of that in Northern Ireland and it didn’t work there. In fact, it made the situation worse,” he said.
“We remain neutral and we will watch to see what impact it will have. The security of our members will be paramount at all sites.”
Frankland has been chosen for the trial because of the number of high-risk prisoners that it holds. The unit could be open by June. The prison, one of the eight highest-security institutions in the country, houses Tanvir Hussain, who planned to blow up flights from Heathrow to the United States using liquid bombs hidden in soft-drink bottles; Dhiren Barot, who masterminded a plot to explode a radioactive “dirty bomb"; and Omar Khyam, who was convicted of planning to blow up the Bluewater shopping centre in Kent.
Michael Adebolajo, who murdered the soldier Lee Rigby, was transferred to Frankland amid fears that he was attempting to radicalise inmates in Belmarsh.
In 2015 a copy of the al-Qaeda magazine Inspire was uncovered during a cell search in the prison.
Jackie Marshall, of the Prison Officers Association, said that staff were undergoing specialist training to deal with extremists.
“What happens in prison tends to reflect what is happening in society,” she said. “There is a problem with radicalisation outside prison and that is reflected inside, so it’s something we have to deal with.
“The unit at Frankland is a separation unit, not a segregation unit, because the prisoners who will be in it are not being punished; they are being held separately.”
A Ministry of Justice spokesman said: “Islamist extremism is a danger to society and a threat to public safety. It has to be defeated wherever it is found. We are committed to confronting and countering the spread of this poisonous ideology in prisons.”