Mystery deepens over IRA man who spied for Britain

Clamour for public inquiry grows after revelation that Gerry Adams's trusted lieutenant was British agent for 20 years

The clamour for a public inquiry has intensified following the revelation that one of Gerry Adams's most trusted lieutenants was a British agent for 20 years.

Denis Donaldson was "outed" as a traitor by Sinn Fein on Friday and thrown out of the party after being acquitted in court of leading an IRA spy ring at Stormont. It was the "Stormontgate" spy scandal that ended Northern Ireland's power-sharing executive three years ago.

Mr Donaldson, who shared a cell block with Mr Adams during the 1970s and was photographed in the Maze prison with the hunger striker Bobby Sands in 1980, this week confessed to spying on Sinn Fein.

The republican charge, backed by Mr Donaldson, is that there was no Sinn Fein or IRA spying operation at Stormont, and that the entire saga was fabricated by Special Branch.

The strong feeling is that the whole Donaldson story has yet to be told. There is even speculation that another long-time agent, planted in Sinn Fein by Special Branch, may be exposed.

Unionists are leading the push for an inquiry. The authorities can be expected to refuse to grant this, but the pressure for an explanation is mounting since Mr Donaldson seems to be the key to recent mysterious events.

When the charges against him were thrown out of court, there were calls for clarification of a statement from the Director of Public Prosecutions that proceeding with the case was not in the public interest. Both Tony Blair and the Secretary of State for Northern Ireland, Peter Hain, said no further information could be provided and that the DPP was a completely independent figure.

Though Mr Donaldson's emergence as an agent is embarrassing for the republicans, Sinn Fein went public with his admission, calculating that it would embarrass the authorities even more.

Mr Donaldson, believed to have held senior rank in both the IRA and Sinn Fein, has expressed remorse and claimed he was "recruited after compromising myself during a vulnerable period in my life".

Despite his insistence that there never was a spy operation at Stormont, the police insist that they broke up a large-scale republican operation which delivered into IRA hands personal details of security force personnel as well as private political correspondence.

The fall-out from Stormontgate was extensive. The affair damaged the overall political situation, the security situation and even public finances. The saga remains inexplicable in that it is difficult to see why anyone could have planned the events as they happened.

It could be that an intelligence agency was attempting an operation that went badly wrong, with unintended consequences. The Northern Ireland Office has rejected all allegations that the police operation at Stormont was for any reason other than to prevent paramilitary intelligence gathering.

Among those seeking more information is the Irish Prime Minister, Bertie Ahern, who said: "If one of Sinn Fein's top administrators in Stormont turns out to be a British spy, this is as bizarre as it gets."

"We have always had our doubts about Stormontgate but I would just like to hear all sides of it before I can pass a judgement on it, and I am not in a position to do that now."

Mr Donaldson seemed to be regarded within Sinn Fein as a safe pair of hands. A journalist who knows him said yesterday: "He was the sort of guy you wouldn't even ask to break a confidence - there was just no point in trying to get him to be indiscreet."