Mr Donaldson, once a leading member of Sinn Féin, was killed in April 2006 shortly after being exposed as an informer for police and British security forces.

Nobody has been convicted north or south of the border in connection with the murder.

A coroner’s inquest into Mr Donaldson’s death has been adjourned 27 times.

The Donaldson family wrote to justice minister Helen McEntee in April 2021 to request the creation of a judge-led commission to examine all information and documentation relating to Mr Donaldson’s murder.

Madden & Finucane Solicitors, representing the Donaldson family, said a response was finally received this week, in which Mrs McEntee said it would not “be prudent” to consider the establishment of a commission of inquiry in light of an “active ongoing criminal investigation by An Garda Síochána”.

In a statement, Mr Donaldson’s daughter Jane said: “The Irish government is publicly demanding an Article 2 compliant approach to legacy cases in the north of Ireland while it continues to refuse to provide an Article 2 compliant investigation into my father’s murder.

“In two decades since my father’s murder, no Irish government minister has been willing to meet my family and account for its double standards and differential treatment.

“Whilst others — like agent Stakeknife — were shielded and shepherded away to safety, my father was left exposed and given no protection. State agencies and officials in both jurisdictions were complicit in that and it is in the public interest to uncover the truth in an open, robust and transparent manner capable of commanding public confidence.”