More than 130 inmates of Irish jails had errors in their sentences that left some spending more time in prison without any explanation.
Two separate internal audits conducted last year found erroneous sentences on prison files and, in one instance, an individual was released after lodging court proceedings against his continued detention.
In response to a parliamentary question from Green Party TD Patrick Costello, Justice Minister Helen McEntee said an initial review of 4,000 prisoners, between February and July 2021, identified 25 prisoners whose sentence was decreased and a further 23 who had their sentence lengthened.
A further review in July 2021 led to 77 prisoners having their sentence increased and six having it decreased.
Mr Costello raised the matter with the minister after a Covid inspection by the Office of the Inspector of Prisons revealed anomalies in Castlerea Prison in Roscommon last year.
A section of the inspector's report notes how a “large number of prisoners” told the inspection team that their release dates had recently been moved “without explanation”.
"For example, one prisoner stated his release date had been moved from January 2022 to June 2022, and another prisoner reported that two months had been added to his sentence,” the report said.
At Castlerea, all but one had their sentence extended.
In her reply to Mr Costello, Ms McEntee said the reasons for inaccurate sentences being calculated included “erroneous start dates where a prisoner had multiple warrants, incorrect linking of consecutive and concurrent warrants, warrants not recorded after appeals, and misinterpretation of warrants”.
The minister also confirmed that it is proposed to begin an external review of the “policies, processes, and procedures in operation for the calculation of prisoner sentences by a suitably qualified person”.
Mr Costello, who was suspended from the Green Party this week for supporting a Sinn Féin motion on the National Maternity Hospital, told thethat he welcomed the external review that will take place.
He also said this issue highlights the need for a strong, independent Inspector of Prisons, given it was brought to the inspector’s attention during a Covid check.
The outgoing Inspector of Prisons told the Justice Minister earlier this year that her decision to leave the job before her contract expired was because of the constant attempts to undermine her office.
"For me, this really shows why prison inspectors need more powers and power to publish their own reports,” Mr Costello said.
“It always raises questions if reports are waiting to be released.”