Brendan McConville is one of two men currently serving a prison sentence for the 2009 murder of PSNI officer Stephen Carroll, for which the Continuity IRA claimed responsibility.

The CCRC last year rejected an application from Mr McConville’s lawyers to have his conviction referred to the Court of Appeal on the basis of revelations about the role of an alleged MI5 agent in the “Justice for Craigavon Two” campaign group prior to an unsuccessful criminal appeal.

Darragh Mackin of Belfast-based Phoenix Law, representing Mr McConville, told The Irish News: “This is a situation whereby an MI5 agent placed himself within the confines of a close family and campaigning circle to ensure that he obtained information with regards to the defence preparations of a high-profile murder case.”

The watchdog’s decision not to refer the case to the Court of Appeal has now been quashed and the case will be reviewed again.

Mr Mackin said: “We intend on engaging with the CCRC in the coming weeks to emphasise the importance on a rehearing of this case in light of the fundamental principles at stake.”

A spokesperson for the CCRC said: “Having considered the arguments made on Mr McConville’s behalf and to ensure absolute fairness, the CCRC has, in line with its published policy on judicial review, offered to take another look at his case.”