A former IRA prisoner said he was instructed to carry out a bombing by Sinn Féin’s Gerry Adams – now a TD for Louth – and Martin McGuinness.
The party has said allegations by Peter Rogers are untrue.
Mr Rogers told the BBC Mr Adams and Mr McGuinness ordered him to transport explosives to Britain in 1980 and said they must be “suffering from Alzheimer’s” if they can’t remember.
Rogers said he expressed concerns at a meeting in Dublin that the liquid explosives were “unstable” and feared he could be killed in a premature explosion or that he might be arrested in possession.
“When I met with them, Gerry wanted to know what the delay was,” Mr Rogers told the BBC when repeating claims first made in the Sunday Independent.
He asked for replacement explosives. He said the pair listened to his comments and then spoke together out of his hearing before taking a decision.
“Gerry said, ‘look Peter, we can’t replace that explosive, you will have to go with what you have and as soon as you can get it across, the better.’ So, as far as I was concerned, I was given a direct order,” said Rogers.
The 69-year-old is a former IRA prisoner who escaped from the Maidstone Prison Ship in 1972.
Shortly after his alleged meeting with the Sinn Féin leaders his van was stopped in Wexford while he was transporting the explosives, with Rogers jailed after shooting and killing Detective Garda Seamus Quaid in the ensuing gun battle on 13 October 1980.
Another officer was injured in the attack.
A Sinn Féin spokesman said: “There is no truth in these allegations. Gerry Adams has already publicly refuted these claims.”
However, Democratic Unionist Party (DUP) East Derry MP Gregory Campbell claimed the republican leaders needed to come clean.
He asked: “How long will they continue their pretence? The terror happened, it is now over.
“They need to admit their part in it, face whatever consequences there may be and move on.”
The Sinn Féin president has always denied being in the IRA, while Mr McGuinness said he left in the early 1970s.
Mr Campbell said: “The latest revelation from former IRA prisoner Peter Rogers that he had been instructed by Gerry Adams and Martin McGuinness to carry out a bombing in England in 1980 is further evidence of Sinn Féin’s attempt to live in denial about their past.”