A Northern Irish prison that holds some of the most dangerous republican paramilitary prisoners has lifted a ban on books about terrorism.

A review by the Northern Ireland Prison Service deemed the ban “not proportionate” and ordered a change of policy, it was announced on Monday.

The review followed a Guardian report in April that Maghaberry prison, outside Lisburn in County Antrim, had prevented inmates gaining access to Unfinished Business: the Politics of ‘Dissident’ Irish Republicanism, written by Marisa McGlinchey, a research fellow in political science at the Centre for Trust, Peace and Social Relations at Coventry University.

The prison service cited a need to provide a “neutral environment”. Critics, including inmates, called the policy unjustified.

Ronnie Armour, the service’s director general, told the BBC the review had prompted a change in policy. He briefed McGlinchey about the changes, which she welcomed.

In a statement, the prison service said it was a “changing organisation and learning organisation” and that new procedures were in place.

“Books and other reading material will now be permitted unless they overtly promote or encourage the commissioning of criminal acts or otherwise break the law. Decisions will be taken on behalf of the governor of each prison, with a review process available at headquarters.”

It remains unclear how many books were banned.

Unfinished Business, published in February by Manchester University Press, is a study of radical republicans who accuse Sinn Féin and the Provisional IRA of accepting partition and selling out the movement. It is based on interviews with about 90 republicans, including inmates at Maghaberry.

The book has been endorsed by the life peer Paul Bew and Richard English, professors at Queen’s University Belfast and experts on Northern Ireland politics.

Relations between Maghaberry prison staff and the several dozen republican dissidents held in Roe block have often been strained, with disputes over Irish-language tuition and full-body searches.

The New IRA murdered two prison guards, David Black in 2012 and Adrian Ismay in 2016. After Black’s killing, inmates reportedly strode around the astro-pitch smoking cigars in celebration.