Of its 1,230 staff, 957 (77 per cent) identified themselves as Protestants and just 166 (13 per cent) identified themselves as Catholics. Nearly 9 per cent did not declare their background.

Ivor Dunne, chair of the Northern Ireland Prison Officers’ Association, told the Belfast Telegraph: “There are three religions in Northern Ireland: Catholic, Protestant and security forces, and the other two can turn on the last one at the drop of a hat.

“I have been in the Prison Service for 30 years and I have never once encountered religious bias. I wouldn’t stand for it. I would encourage anyone from any religion to join the Prison Service.”

A spokesperson for the Prison Service said it “is committed to ensure that as an organisation it reflects the community it serves”.

The spokesperson added: “In any of its recruitment campaigns the Prison Service seek to encourage applications from all sections of the community. Ultimately appointments to the NIPS are made on merit.”