Martin Ferris has claimed he has information on Fianna Fáil and other political parties that was “more than politically embarrassing”.

The Sinn Féin TD said there were things he could say that would highly embarrass Micheál Martin and Fianna Fáil if he wished to do so.

However, speaking on Radio Kerry on Thursday, Mr Ferris denied he was making a threat and said he would not reveal the information.

Mr Ferris also said he wished he hadn't written about Brian Stack in his biography. He was asked on Thursday about the terms he had used in the book, published in 2005, to describe the former prison officer, whom he had encountered while incarcerated in Portlaoise prison.

“I wish it wasn’t in the book . . . but it was,” Mr Ferris said.

Mr Stack was the chief prison officer in Portlaoise prison when he was shot in the neck, aged 48, on March 25th, 1983. He was attacked after leaving an amateur boxing contest at the National Stadium in Dublin. The father of three was left paralysed and brain-damaged and lived for 18 months after the attack.

On Kerry local radio on Thursday, Mr Ferris went on to say that what he said about “prison management” at Portlaoise in the book was “very, very consistent” with what two prison officers had said at a conference in 1982. “And I’ll quote from it if you wish, “ he told presenter Jerry O’Sullivan.

Mr Ferris said a friend of his had died tragically, and others had suffered, as a consequence of their time in Portlaoise. “There’s an awful lot of victims here,” the TD said.

He said he was in no way condoning the murder of Mr Stack.