'Security force spy' to be named

MP David Simpson said he would use parliamentary privilege to name the alleged mole, a move which could destabilise relations in the province's power-sharing executive.

The politician under suspicion is well known and Mr Simpson added that his intervention would not come before the autumn when the Assembly will have returned after the summer break.

"It will be October time before we get to the nitty-gritty of it. At this moment in time we are keeping our powder dry."

The murder victim in the case referred to by the DUP is Frederick Lutton, 40, a former part-time member of the Royal Ulster Constabulary reserve, shot dead on May 1 1979, in County Tyrone.

Mr Lutton was a caretaker for the National Trust, killed as he left his car to lock the gates of its premises in Moy.

He was a cousin of Mr Simpson.

The partnership between Sinn Fein and the Reverend Iain Paisley's DUP has worked well since the May restoration of devolved government.

The last time the Assembly was suspended, in October 2002, followed the exposure of Sinn Fein official Denis Donaldson, 56, as a police agent after detectives arrested him for alleged intelligence-gathering at Stormont.

He was later shot dead in County Donegal.