The Taoiseach and British Prime Minister will today try to determine what concessions republicans and Ulster Unionists are prepared to make on IRA arms and policing.
Mr Ahern and Mr Blair expect that the main "pressure point" of the intensive negotiations, which started yesterday in Weston Park in Staffordshire, will be reached tonight or early tomorrow when republicans will be asked to declare what moves they can make on IRA arms, and the UUP will be asked whether it will tolerate further amendments to police legislation.
"It is getting close to the stage when the main parties must show the colour of their money on the key issues of IRA weapons and policing," said one senior participant in the talks last night.
The pro-agreement parties were locked in discussions with the British and Irish leaders from yesterday afternoon to late last night.
The Alliance party, the Progressive Unionist Party, the Ulster Democratic Party and the Woman's Coalition concluded their participation in the talks around tea time, leaving the UUP, Sinn Fein and the SDLP to focus on the key issues. .
After leaving the talks, Mr Billy Hutchinson of the PUP gave a thumbs-down sign, while party colleague Mr David Ervine complained that the smaller parties were being sidelined.
The governments believe that the chances of a deal lie with the pro-agreement parties which have executive positions - the UUP, the SDLP and Sinn Fein - even though they do not want to alienate the smaller groupings.
One talks source said yesterday's business was to allow the leaders and the parties to review progress to date, and to prepare the way for more serious engagement today.
"Everybody is serious and determined, but we have yet to get to the stage where the parties will reveal their bottom lines," he said.
The Sinn Fein president, Mr Gerry Adams, is insisting that it is not for Sinn Fein to deliver on decommissioning, while Mr Trimble is attempting to portray the negotiations as focusing on a single issue, that of IRA arms.
"There was always going to be a moment of truth in this process when we would find out whether the republicans were prepared to discard their Armalites," he said outside Weston Park. "You cannot have a democratic process where one party retains weapons."
Lagan Valley MP, Mr Jeffrey Donaldson, who is part of the UUP talks team, insisted that unionists would not accept any further tampering with the Police Act.
Speculation that a breakthrough might be imminent intensified briefly when it emerged that former US President Mr Bill Clinton had spent Sunday night at Mr Blair's country residence in Chequers.
When it became clear Mr Clinton would not be joining the talks, there were suggestions that he would be ready to make telephone calls if that was considered likely to help.
However, usually reliable sources later maintained Mr Clinton's presence at this time was "entirely coincidental".
