A former IRA prisoner said he was instructed to carry out a bombing by Sinn Féin's Gerry Adams 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.
The 69-year-old is a former IRA prisoner who escaped from the Maidstone Prison Ship in 1972.
Eight years later, he was jailed in Ireland for the IRA murder of a garda.
Detective Garda Seamus Quaid was shot and killed after his patrol stopped a vehicle in Co Wexford 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."
But 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."