Claims that the IRA has gone away are a “blatant lie”, says the son of the only prison officer murdered in the Republic during the Troubles.

His comments came after Minister for Justice Frances Fitzgerald asked the Garda Commissioner to work with the PSNI and carry out a fresh assessment of the operations of the IRA in light of evidence emerging from the investigation into the death in Belfast of Republican Kevin McGuigan.

Austin Stack and his brother Oliver were driven to an undisclosed location in a blacked out van two years ago to get an IRA statement admitting the organisation murdered their father Brian.

The meeting, organised by Sinn Féin leader Gerry Adams, proves the IRA still existed then, claims Mr Stack.

“The facts are that my brother and I actually met the IRA, so for Sinn Féin to now claim that they went away after the ceasefire is a blatant lie,” he said.

The brothers held talks with Mr Adams and a former IRA commander for weeks in 2013 as part of a long campaign to secure a confession.

At the time, Mr Adams said he accompanied the two brothers to a meeting with an ex-Provisional IRA boss, who admitted the IRA shot their father in the back of the neck on March 25th, 1983.

Brian Stack (48), who was the chief prison officer in Portlaoise, was shot in the neck on March 25th, 1983, after leaving an amateur boxing contest at the National Stadium in Dublin.

The father of three was left paralysed and brain-damaged. He lived for 18 months after the attack. The IRA had always denied it was behind the killing.

Mr Stack said denials that the IRA still exist “bear no relevance to the hard facts”.

"I met the IRA in August 2013, the IRA used its structures to get me information, Gerry Adams organised this meeting, are Adams and (Sinn Féin TD) Brian Stanley now claiming that this meeting never happened?" he added.

His sons were driven to a bungalow at an undisclosed location in a blacked out van from the M1, where they were handed the IRA statement, printed up on a typewriter, and told to transcribe it.

The statement said their father’s killing was “not authorised by the IRA leadership and for this reason the IRA denied any involvement”.

It added that the Provisional IRA killers involved were acting under orders and that the IRA was responsible.

Earlier on Tuesday, Ms Fitzgerald said making organisational judgments about the IRA was “complicated by the fact that many, if not all, members” of the group were also members of Sinn Féin.

Her comments came as PSNI detectives investigating the murder of Mr McGuigan arrested a 47-year-old man in Belfast city centre. Mr McGuigan (53) was shot dead outside his home in Comber Court in the republican area of Short Strand on August 12th.

Ms Fitzgerald was speaking following allegations of IRA involvement in the killing of Mr McGuigan. She said making organisational judgements about the IRA was “complicated by the fact that many, if not all, members” of the group were also members of Sinn Féin.

In a statement, the Minister said there was no doubt people who have been associated with the IRA “have been - and continue to be - involved in the most serious crime” and that neither Gerry Adams nor Sinn Féin could “wash their hands of responsibility for that”.

However, Ms Fitzgerald said it would be “quite wrong” to say the Provisional IRA continues to exist as if nothing has changed since the peace process.

Sinn Féin said the assessment of the status of the Provisional IRA will prove it no longer exists as an organisation. Sinn Féin Laois-Offaly TD Brian Stanley said the party has “no problem” with such an assessment.

“We have no problem with that, we welcome that. It will show that the army was stood down 10 years ago, that it doesn’t exist. That the mainstream of republicanism became involved totally in the republican process and that’s where it’s going and that’s what people are busy doing within Sinn Féin.”

However, Mr Stanley criticised Tánaiste Joan Burton for a statement she made in which she said the IRA was still linked to “murdering and racketeering” and that Sinn Féin cannot deny all knowledge of its criminality or existence.

He said Ms Burton is using the “silly season” and the killing of two people to criticise Sinn Féin.

Ms Burton earlier said she did not believe Mr Adams when he said the IRA has gone away and left the stage. “When people leave the stage, that leaves the question where do they go? Are they at the side of the stage or at the back of the stage?” she said.

Additional: PA