The Taoiseach, Mr Ahern, is to meet the DUP led by the Rev Ian Paisley in London tomorrow morning for talks which could signal a deal within a week to restore Stormont.
Details of the meeting emerged after a day of intense discussions centring on the Democratic Unionists, Sinn Féin and government officials. Mr Martin McGuinness, Sinn Féin's chief negotiator, said talks involving his party were "productive and useful" and that discussions were "clearly in final defining moments".
The DUP said it would meet the Northern Secretary, Mr Paul Murphy, today in London regarding an investment package which could help secure any political deal.
A DUP source said a reported figure of £1 billion was "a little conservative", but added: "The mother of all deals will have the mother of all prices."
Asked about this, Sinn Féin said it wanted the British security budget in Northern Ireland redirected to target deprivation.
With Democratic Unionists insisting they were on course for "a fair deal" to restore Stormont, Sinn Féin said republicans needed confirmation from the two governments that the DUP would share power. They also wanted Dublin and London to guarantee that any deal was "rooted in the Good Friday agreement".
Contacts between the party and officials, said Mr McGuinness, would aim to settle "outstanding issues of importance to republicans".
The success or otherwise of the current intensive push for a settlement would be known by the Taoiseach's Friday deadline.
Mr McGuinness insisted the Belfast Agreement was an internationally binding treaty and that its provisions could not be subject to what he called a one-party veto.
An official spokesman for the British Prime Minister, Mr Tony Blair, confirmed this was a crucial week but said he would "not provide a running commentary" on progress. "It can and should be made," he said last night. "It's now all down to the parties."
Various sources placed particular emphasis on Dr Paisley's role in talks and on his meeting with Mr Ahern tomorrow.
Officials in Dublin and London would not be drawn on the significance of the Paisley-Ahern talks, preferring to view them in the context of an overall effort to secure progress.
However, it is understood that the stance taken by the 78-year- old DUP leader in relation to any deal could prove pivotal.
His spokesman, speaking last night after a series of party meetings, indicated the DUP "was neither up nor down" regarding prospects of success.
It wanted clarification on a series of points raised during talks with officials and "was still on for a fair deal".
No one contacted yesterday by The Irish Times wanted to anticipate failure.
However, Mr McGuinness said it was clear that while the two governments wanted a successful conclusion by the end of the month, they would "have to move on decisively" if deadlock was not broken.
The SDLP met the Government for talks in Dublin yesterday having been briefed on the proposals to restore Stormont.