Sinn Féin and the Ulster Unionists are now engaged in serious negotiation of a draft British-Irish agreement on "acts of completion" covering all outstanding issues in the peace process.
That was the official assessment last night as Sinn Féin leaders Mr Gerry Adams and Mr Martin McGuinness continued talks with British and Irish officials in London. It is understood the Ulster Unionists were not directly involved in yesterday's discussions, although Downing Street has maintained close contact with the UUP leader, Mr David Trimble, throughout the week.
Officials confirmed a readiness to continue the talking throughout the weekend in preparation for Monday's summit meeting with the pro-agreement parties in Belfast to be hosted by the British Prime Minister, Mr Tony Blair, and the Taoiseach, Mr Ahern.
Although insisting they still "genuinely don't know" whether agreement can be reached, Whitehall sources said they had the feeling "that Monday will be a serious day, a big day" which would have "a dynamic of its own."
Downing Street has stopped short of setting Monday as an absolute "deadline". At the same time, it is being made clear Mr Blair is travelling to Belfast in search of "a result" and expects to conclude Monday's marathon session at least with a clear sense of the prospects for success or failure.
Confirming the "serious" nature of the Ulster Unionist/Sinn Féin engagement on the issues, Irish sources reflected Whitehall's official caution, saying they were "hopeful" rather than "optimistic" about Monday's summit.
At the same time, there was a reminder of ambitions for this negotiation, with confirmation of the British government's desire to secure an end to the suspension of the Stormont Assembly and an Ulster Unionist return to power-sharing with Sinn Féin for the short period before dissolution on March 21st and the election of the new Assembly scheduled for May 1st.
London accepts that the possibility of Mr Trimble risking a formal split in the UUP depends on the clarity of IRA commitments to redefine and extend the definition of their cessation of military operations.
While apparently still awaiting details of any IRA offer, British and Irish officials have spent much of this week seeking a formula to satisfy Mr Trimble's demands on the monitoring of paramilitary ceasefires, and "sanctions" to be used against any party deemed in breach of a commitment to exclusively peaceful means.
Usually reliable Sinn Féin sources said last night that agreement could still be reached next week.
Fiercely rejecting earlier Dublin and London suggestions of republican foot-dragging, the sources repeated that Sinn Féin has yet to see a comprehensive and timetabled British plan for the implementation of all outstanding commitments entered into under the Belfast Agreement.