The absolute deadline Tony Blair has attached to these talks is finally upon all the parties to these negotiations.

By the end of Wednesday, the republican movement must have made genuine commitments to the decommissioning of weapons by May of next year - and the Ulster Unionists will have had to accept their promises and allow Sinn Fein to step into devolved government with them.

It means both sides accepting a substantial shift in the positions they have stuck to rigidly for more than a year.

Anything less than that would appear to mean failure and huge uncertainty for the Good Friday Agreement.

The mood music yesterday was significantly more upbeat than in recent days and weeks but even then the leader of the Ulster Unionists, David Trimble, ended his day of talks declaring that very little actual progress had been made.

David Trimble: Played down reports of progress

"It is a pity," he said, "we are two days into this and we still have not heard any clear indications from republicans that they will carry out their obligations."

What there has been, though, is close contact between Sinn Fein's leadership and senior representatives of the IRA.

It points to a genuine effort from Sinn Fein to see if the IRA can provide the sort of commitments the two prime ministers have insisted upon. If it can, it would justify the decision by Tony Blair and Bertie Ahern to delay publication of the report by General John de Chastelain - due on Tuesday - which indicates the readiness of parties and paramilitary groups to pursue full decommissioning.

Indeed, by now that report may already be out of date, as it is based on replies given to the General last week.

So make or break has at last arrived. Tony Blair has made it clear he has no Plan B if this ends in deadlock but it seems inevitable that certain sanctions would have to be imposed.

Tony Blair: Reflecting on difficulties

The assembly may be suspended. Questions would be raised about the continuing early release of prisoners, and further demands might be made by different parties to this peace process. That would amount to a spiral of renewed distrust.

As Monica McWilliams, a member of the Women's Coalition put it: "This is a house of cards. The Good Friday Agreement stands as a whole, it will fall as a whole. We are in it for everything or nothing."