SDLP sources say they have also been briefed that IRA decommissioning was “due any time now”, but doubt if agreement between the DUP and Sinn Fein will follow.

“Continued direct rule with an enhanced cross-border dimension, seems most likely and that is the basket we are putting most of our eggs in,” a senior SDLP figure said.

Fears that last week’s loyalist violence would delay the IRA move have been dismissed, with authoritative sources saying “the process is completely on track”.

Gerry Adams, the Sinn Fein leader, was in Washington to brief senior administration officials and speak at a conference hosted by Bill Clinton.

He said: “I am confident the commitment made by the IRA will be honoured” despite the loyalist unrest.

“I think that it opens up an enormous opportunity for all of us but also presents a huge challenge,” he added.

“Our understanding is that the IRA has made a tactical decision to move out of the equation,” Donaldson said. “That has put the spotlight on the Ulster Defence Association and the Ulster Volunteer Force. These loyalist paramilitaries have been flexing their muscles, saying ‘We haven’t gone away you know’. They want to stake their claim for concessions.”

The IRA announced on July 28 that it had formally abandoned violence and intended to decommission all its weapons.

This prompted reciprocal concessions from the British government including the dismantling of military bases, a two-year timetable for the disbandment of the home service battalions of the Royal Irish Regiment, and a projected halving of troop numbers in Northern Ireland to a garrison strength of approximately 5,000 soldiers.

The IRA arsenal is believed to have been located in at least three bunkers just south of the border. The first bunker to be decommissioned is believed to have been in Donegal near the border with Derry. For the past three weeks arms have been collected from IRA units in Northern Ireland in preparation for the move.

The decommissioning, which consists of covering the weapons with concrete, is supervised by at least two of the three Independent International Commission on Decommissioning officials and by two independent clerical witnesses.

The political impact of the gesture will depend on how much detail the IRA allows the witnesses to make public.

But even with minimal detail, any announcement from de Chastelain that decommissioning has been completed will put pressure on the loyalist para-militaries to reciprocate.

The DUP will also be under increased pressure to share power with Sinn Fein within a reasonable period of time and to enter into serious negotiations.