The Taoiseach, Mr Ahern, and the British Prime Minister, Mr Tony Blair, expect the Rev Ian Paisley and Mr Gerry Adams to have reached "their point of decision" today on whether to accept the Irish and British governments' blueprint for restoring devolution.
Last night all sides agreed that high-powered talks centred on London today involving the Irish and British leaders and Dr Paisley and Mr Adams are "critical", but none of the senior protagonists was willing to call the outcome.
The governments however will take a degree of comfort from some positive comments from the DUP leader, the Rev Ian Paisley, last night.
Dr Paisley said: "We have made progress. We have made greater progress than I thought we would have made - I admit that." He had met the Northern Secretary, Mr Paul Murphy, in London to discuss a potential £1 billion peace dividend if the talks succeed.
He acknowledged the consequences if these negotiations fail. "If Northern Ireland is going to get a fair deal, and it has not got a fair deal so far, it will get a fair deal now," he said. "If we miss the opportunity we will never get this back."
Dr Paisley however also said he had received no commitments from the IRA on the DUP's demand for a visual element to decommissioning. "We have got nothing from the IRA. The IRA have given us no promises whatsoever."
A senior Sinn Féin source last night was also relatively positive. "We think a deal can be done, but the next few days will determine the final outcome," he said. "Everything should be clear in the next four or five days."
Sinn Féin's ruling ardchomhairle will consider the proposals at a meeting in Dublin tomorrow, while the 80-100 member DUP executive will deliberate on the blueprint in Belfast on Friday night. These could be the determining meetings as to whether the parties will endorse, or rebuff, the proposals.
This morning the Taoiseach will first meet Dr Paisley, then Mr Adams and Sinn Féin's chief negotiator, Mr Martin McGuinness, in the Irish Embassy in London. At 11.30 a.m. Mr Ahern will meet Mr Blair in Downing Street.
Ahead of the meeting between Mr Ahern and Mr Blair, Dr Paisley will also meet the Prime Minister in Downing Street. Sinn Féin said there was no scheduled meeting between Mr Adams and Mr Blair, but that Mr Adams and Mr McGuinness would hold talks with senior Irish and British officials in London today.
The sequence of the meetings is viewed as important. Sources said neither Mr Ahern nor Mr Blair were expecting definitive yes or no answers from Dr Paisley and Mr Adams today, but they did expect them to have arrived at their "point of decision".
They expected at this morning's meetings that the DUP and Sinn Féin leaders will at least have strongly signalled whether or not they can accept the governments' blueprint.
If these signals are negative then Mr Ahern and Mr Blair may feel compelled to further advance their "Plan B" option for failure.
"The realpolitik of failure will be addressed," a senior source said, indicating that rejection would carry a political cost.
"Plan B" could involve triggering the d'Hondt mechanism for appointing ministers to an Executive, thereby putting it up to the parties who had rejected the document to boycott or sit in the Executive.
It could also involve calling fresh Assembly elections or strengthening the British-Irish dimension of the Belfast Agreement to try to ensure that the IRA's purported offer to end activity and decommission is not lost.
