Details of the alleged spy ring, the existence of which has always been denied by Sinn Fein, have been given to the Sunday Tribune by a member of the party's Stormont team. They suggest that the spy ring was very active and was not a fabrication by British 'securocrats', as Sinn Fein has claimed.

The source claimed the party's Assembly representatives and administrative staff at the time knew of the spy ring's existence and were asked to gather intelligence on unionist politicians. He described the party's ongoing denials that no Sinn Fein spy ring existed as "completely untrue" and said it was time to tell the truth about events at Stormont.

The source claimed the spy ring was "an open secret" among the Sinn Fein team and began a year before the 2002 arrest of Denis Donaldson, the party's Stormont administrator who was outed as a British agent last month.

Donaldson wasn't the spy ring's leader or organiser.

According to the source, an Assembly member, whose name is known to the Sunday Tribune, instructed other Sinn Fein representatives and staff to gather information on unionist Assembly members.

"We were told to find out any weaknesses they might have . . . how much they drank, where they drank, who they drank with, " the source said.

"We were told to find out if they had a gambling problem or money difficulties, if they cheated on their wives, who they were sleeping with, if any of them were gay."

Some of the Sinn Fein members and employees cooperated but others refused. Ulster Unionist politicians were the targets as the DUP wouldn't talk to Sinn Fein. "Barriers were breaking down between us and the UUP. People would find themselves naturally chatting to UUP colleagues during a tea-break in a committee meeting or in the members' bar, " the source said.

Information gathered was relayed back to the Assembly member organising the spy ring, who liaised with a Sinn Fein staff member whose name is known to the Sunday Tribune.

It is understood the Sinn Fein staff member then reported the information to the director of intelligence of the IRA's GHQ (general headquarters) staff, the west Belfast man who masterminded the Northern Bank robbery.

Some Assembly members objected to the spy ring, believing it contradicted Sinn Fein's stated aim of building trust with unionists.

The source stressed unionists were never in danger of assassination from the IRA.

"The operation was to build intelligence and to placate foot-soldiers in the movement who had doubts about even entering Stormont. It was to relay the impression 'we might be in here but the war goes on'."

The source also claimed that Donaldson had accessed pornographic material at Stormont on computers used by Sinn Fein, but had stopped after complaints from a female member of Sinn Fein's staff who feared that his internet habits would damage the party if they were discovered.

A Sinn Fein spokesman yesterday denied the party operated a spy ring at Stormont.

"There was a spy ring, at the centre of which was a British agent, Denis Donaldson, " he said.