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.