7% of inmates locked up for 23 hours

Almost 200 prisoners are locked in their cells for 23 hours a day — a rise of 10% in just over six months.

The increase in the number of people under the most restricted prison regime parallels a similar rise in assaults in jails last year. Prison bosses link much of the increased use of protection with gang feuds.

Last May, Prison Service director general Martin Donnellan said there were up to 22 criminal factions in some prisons. He said it was “a challenge” to manage them.