In his first comments since a Dublin Sunday newspaper named him as a British agent, Mr McGuinness told reporters at Stormont that the allegations were “hooey” and that he was “a million per cent” certain that nothing would ever be proved against him.

The former Stormont Education Minister and Provisional IRA commander sounded at moments as if his voice was about to break with emotion as he rejected the accusations.

The claims were based on the verification, by a former Army intelligence officer, of an alleged transcript of a conversation between an IRA member and his MI6 handler.

Mr McGuinness was flanked by fellow Sinn Fein members of the Northern Ireland Assembly. But a notable absence was Gerry Adams, the party’s president. Mr McGuinness said: “I am a million per cent confident no one will ever produce anything against me. I have worked all of my adult life as an Irish republican.

“Many of my comrades have been killed. Many IRA volunteers have been killed and I, of course, knew many of them as many of you well know.

“Under no circumstances will I ever be concerned about anybody throwing anything up at me which will strike against me. It is not even a remote possibility.”

The allegations against Mr McGuinness were made by a former army intelligence officer who uses the pseudonym Martin Ingram.

The former member of the Army’s controversial Force Research Unit, that ran agents inside paramilitary groups, is credited with exposing Freddie Scappaticci, a senior Belfast republican, as an agent whose codename was Stakeknife, and who operated at the heart of the Provisional IRA.

Mr Scappaticci denied the allegations but later fled his West Belfast home. Mr Ingram’s claim, which was published in the Sunday World, also followed hard on the unmasking by the Sinn Fein leader, Gerry Adams, last December, of the party’s head of administration at Stormont, Denis Donaldson, as a spy. Donaldson admitted that he had spied for British Intelligence and Special Branch in a confession broadcast on Irish television and then went into hiding. Last month he was murdered at his hideaway, a remote cottage in Glenties, Co Donegal.

Mr McGuinness added: “The allegations are a load of rubbish. They are total and absolute nonsense and they are hooey of the worst kind.

“Now you would need to have nerves of steel to be part of a Sinn Fein leadership which has had to take the sort of muck and abuse thrown at us over the course of many years, but we are in positions of leadership. If you don’t like the heat, you get out of the kitchen. We have never jumped out of the kitchen. We will stay in this process to the bitter end.”

He said that he had known for some time that elements within the DUP were behind attempts to spread claims that he was working for British intelligence.

He said that Willie McCrea, the DUP MP for South Antrim, had “raised these unfounded allegations” in the House of Commons in February. “No one paid them any attention.”

He added: “I have to say given all that we went through in 2004, it was quite clear then that there were elements within the DUP who were out to sabotage any prospect of an agreement between Sinn Fein and the DUP.

“Here we are at a very critical stage of the process and elements of the DUP are doing their damnedest to try and undermine the prospect of trying to get these institutions up.”

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