The British Prime Minister, Mr Tony Blair, and the Taoiseach, Mr Ahern, will defy the DUP leader, the Rev Ian Paisley, when they fly to Belfast today to publish their proposals for restoring the Stormont Assembly.
However, the precise terms of an expected IRA statement will be crucial to the development of any alternative British-Irish strategy for advancing the political process in the North if the DUP refuses to conclude an early power-sharing deal with Sinn Féin.
At the same time - while the focus last night remained on unresolved issues concerning IRA weapons decommissioning - the Ulster Unionists have signalled a growing political threat to any new deal over proposals to meet Sinn Féin demands that Northern Ireland MPs and MEPs be given speaking rights in the Dáil and the Seanad.
No 10 Downing Street last night refused to be drawn on any "Plan B" scenarios, or about the period of "reflection" it will allow the parties following today's events. However, Mr Blair is expected to underline his determination that the issue of restoring a devolved administration at Stormont cannot be left until after a British general election.
While No 10 again declined to comment, senior British sources admitted that they are not expecting the IRA to concede the DUP demand for photographic evidence of future weapons decommissioning, at least at this point.
The sources accepted the general view that this was the import of the assertion by the Sinn Féin president, Mr Gerry Adams, yesterday that the IRA would not allow itself "to be humiliated". The sources also acknowledged they did not know if the IRA had ever actually considered agreeing to photographs being taken.
The British-Irish paper to be published in Belfast will set out the view of Mr Blair and the Taoiseach as to how the issue of a photographic record could have been dealt with as a contribution to greater transparency and public confidence in the decommissioning process.
However, Mr Blair and Mr Ahern are hoping for an IRA statement confirming acceptance of other key elements of their proposal, which is understood to provide for:
the "front-loading" of IRA decommissioning
confirmation by Dr Paisley and Mr Adams of their nominees for first and deputy first minister coinciding with a first act of decommissioning some 10 days after any political agreement
legislation to end the suspension of the Stormont Assembly in January, paving the way for the Assembly to sit in "shadow" form prior to the appointment of a new power-sharing executive to assume office in March
the completion of intensive talks on the modalities for the devolution of policing and justice powers by the end of February
the appointment of the two clergymen, already identified by the governments, to verify the decommissioning
publication of an inventory of weapons to be decommissioned, and a final listing of weapons destroyed at the end of the process.