The Taoiseach, Mr Ahern, and the British Prime Minister, Mr Blair, seem likely to return to Belfast next week in a joint effort to avert a full-blown crisis in the peace process extending over Christmas and into the New Year.
The decommissioning issue was forcing itself back to the top of the political agenda last night, as the Ulster Unionists prepared to back Conservative demands in a Commons debate this afternoon for a halt to prisoner releases "until there has been substantial and verifiable decommissioning" of paramilitary weapons.
At the same time, tensions between the Ulster Unionists and the Government increased as it became clear that the Taoiseach regards the creation of a North-South implementation body dealing with the Irish language as a crucial issue in negotiations which he candidly told the Dail "have not moved an inch in four weeks".
Mr Ahern and Mr Blair will review a worsening situation on the margins of the European summit in Vienna this weekend. But sources refused to discount a prime-ministerial initiative as Mr Seamus Mallon, the Deputy First Minister, warned that failure to reach agreement on key issues by Monday or Tuesday of next week could delay the implementation of the Belfast Agreement until after its first anniversary, which falls next April.
A day of intensive talks in London and Dublin - billed as a renewed attempt by Mr Blair and Mr Ahern to restore momentum to the process after the failures and recriminations of last week - if anything underlined a widening gap between unionist and nationalist parties on the immediate issues of the ministerial line-up of the Northern Ireland executive and the remit and number of North-South implementation bodies.
During more than an hour of talks with the Prime Minister at 10 Downing Street, Mr John Taylor, the Ulster Unionist Party's deputy leader, insisted that his Assembly colleagues would only agree the creation of six implementation bodies. And he again made clear his view that Ulster Unionist acceptance of nationalist and republican demands for a 10-member executive was conditional upon this.
With the issue on implementation bodies apparently reduced, at least in Downing Street's mind, to a choice between "six or seven", the Ulster Unionists have been insisting the SDLP must in effect choose between tourism and trade and business development. But Mr Mallon stood by his insistence that he last week secured agreement for a total of eight implementation bodies.
At the same time it emerged that Mr Ahern does not consider a body dealing with Irish language issues as something to be traded for either of the other two from the SDLP's "wish list".
Officials on both sides hold out the possibility that the conflicting Ulster Unionist and SDLP positions might eventually be reconciled by placing eight subjects within the remit of six designated bodies.
But Mr Taylor firmly ruled this option out, insisting the proposed bodies must be subject-specific.
In contrast to the gloom attending Mr Ahern's talks with Mr Mallon and Mr Martin McGuinness, Mr Taylor emerged from his meeting with Mr Blair maintaining progress had been made and expressing hope that the issues might be "sorted out" in time for Mr David Trimble's return to the North next Monday, and subsequent approval by the UUP's Assembly party.
At the same time Mr Taylor told The Irish Times: "I still see a possibility for a major collapse of the whole operation." And he reflected on the reason for the reluctance of many of his colleagues to agree the next steps in the process, asserting: "None of this can come into practice involving Sinn Fein unless there is prior decommissioning. That remains our bottom line. We can talk morning, noon and night about the number of implementation bodies, about the number of ministers that will be in the executive of the Assembly.
"None of that will happen involving Sinn Fein until there is decommissioning."
It is understood that at their meeting last Thursday, and again on Monday, a number of UUP Assembly members questioned the leadership's assurance that agreement on the ministerial line-up of the executive could be "parked" pending decommissioning, and would not automatically trigger the D'Hondte mechanism for the distribution of ministerial portfolios.
Mr Trimble is believed to have been consulted by the Conservative front bench about the terms of the motion it has tabled for this afternoon's Commons debate criticising the British government for a failure to ensure "parallel progress" on decommissioning and prisoner releases.