Ulster Unionist leader David Trimble began the process of pulling his party's ministers out of government after losing a key vote in the Belfast Assembly.
His action is expected to mean the closure of the assembly within weeks in the absence of some major last-minute act of arms decommissioning by the IRA. It now seems doomed to face indefinite suspension along with other institutions of the Good Friday Agreement.
Mr Trimble lost the vote because republicans and nationalists refused to back his motion attempting to have Sinn Fein thrown out of the cross-community executive.
A phased Ulster Unionist withdrawal from the local administration is now due to take place over the next two weeks, leaving London with little option but to put the devolved government into cold storage.
The huge questions in Anglo-Irish politics will then centre on how and when the institutions might be revived, and whether the overall peace process might unravel in the meantime.
The nationalist SDLP made it clear yesterday that they would not support Mr Trimble's motion to exclude Sinn Fein, ensuring the defeat of the move, which for success required both Unionist and nationalist support.
The SDLP's new leader-elect, Mark Durkan, called for decommissioning. He said of the Unionist plan to close down the Assembly: "It's as if they are saying that because there's a problem with someone on the bus they are going to crash it. They may think that they are going to take the bus into a ditch. They could very well take it over the cliff."
Mr Trimble told the Assembly that his party's three ministers would first withdraw from the executive, refusing to attend its meetings. This would mean the executive could not function. Next Unionist ministers would resign. Mr Trimble declared: "This procedure will be followed with the objective of bringing about the complete and indefinite suspension of this Assembly."
He said he would announce the precise arrangements for the resignations at the beginning of next week.
Mr Trimble said republicans had had ample opportunity to leave their violent past behind, adding: "The simple fact of retaining a private army in itself indicates there is not a commitment to exclusively peaceful and democratic means."
Sinn Fein president Gerry Adams said there was no basis in the Good Friday Agreement for the exclusion of his party. He added: "We have honoured every commitment which we have made and we have tried to play a positive and leadership role in the peace process." Mr Adams said he believed the motion was not about IRA decommissioning: "It is about the battle for the leadership of Unionism at this difficult time."
Meanwhile the chairman of the Prison Officers' Association said he had no doubt that paramilitaries were responsible for an attack on the home of one of his members.
A prison officer's teenage daughter was alone at the family home in Portadown, Co Armagh, when a gang of men forced their way in and set the house on fire. She suffered shock and the effects of smoke inhalation.
Finlay Spratt said: "We are supposed to have a peace process but the reality is that prison officers and their families are not getting the benefit. People in Northern Ireland are still being terrorised by what I can only call thugs.'
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