The identity of the senior party member at the centre of the allegations is now an open secret after he was named on several internet blog sites.

Upper Bann DUP MP David Simpson has also threatened to name him under legal privilege in the House of Commons.

The Sinn Fein man is accused of being involved in the murder of former RUC reservist Frederick ‘Eric’ Lutton near Moy in Co Armagh in 1979.

Mr Lutton’s son Nigel has made an official complaint to the Police Ombudsman and said he has information from former RUC officers about a cover-up of the killing.

The former police officers have been asked by the Police Ombudsman’s office not to speak to the media for fear or prejudicing any investigation.

It’s thought the Ombudsman plans to move rapidly to investigate the claims the Sinn Fein member was allowed to escape justice because he agreed to spy on the IRA for the security forces.

Sinn Fein yesterday hit out at the claims, labelling them “baseless” and accusing Mr Simpson of hiding behind parliamentary privilege.

The latest claims come after the Denis Donaldson affair, which brought down the last Executive.

The senior Sinn Fein official was exposed as a long-term British agent and later shot dead at an isolated cottage in Co Donegal.

Willie Frazer of victims’ pressure group FAIR says it time for republicans to face up to their involvement in collusion.

“Now the harsh reality for republicans is that for years key members of their organisation were in the employ of the British government.

“The question is no longer if the Provos were infiltrated but for how long, by how many and what were the results.”

He says it’s time victims were given answers about the level of security force collusion with the IRA.

“Now is the time for truth and justice and as victims we demand both.

“In areas like south Armagh we demand the truth about the involvement of British agents with the PIRA and the passing of information on local security force members who were subsequently murdered.”