Senior Ulster Unionists say imminent British proposals for the full implementation of the Belfast Agreement "will almost certainly fail" to secure Mr David Trimble's return next month as First Minister.
And there is continuing speculation in unionist and republican circles that London may be forced to rely on a legal technicality which it is thought would effectively extend the August 12th deadline for the election of a First and Deputy First Minister of the Northern Ireland Executive by a further six weeks.
That could result in a negotiation of Mr Tony Blair's package of measures - agreed with the Taoiseach, Mr Ahern, - into the autumn, despite suggestions the two leaders would offer their agreed position to the parties on a "take-it-or-leave-it" basis.
The UUP leadership's expectation remains that the "failure" of the proposed package would result in "suspension followed by review" of the agreement by the August 12th deadline for Mr Trimble's re-election or replacement as First Minister.
However, unionist and Sinn Fein sources say they have been alerted to a legal loophole in the Northern Ireland Act which might permit a one-day "suspension" of the agreement to be followed by a further six-week deadline for resolving the threat to the Executive's existence.
One unionist source last night said he thought Mr Blair may be tempted "to buy a little bit of time" by this route, while adding his belief that "we'll end up with the same result".
Sinn Fein sources have expressed the view that, if legally possible, "politically speaking it's something that would seem to be do-able just the once".
Other sources, meanwhile, cast doubt on the possibility of any further extension of the statutory deadline, pointing to a provision of the 2001 Act, stipulating that following any suspension "as soon as is reasonably practicable the Secretary of State must take steps to initiate a review under the validation, implementation and review section of the Belfast Agreement".
What was not in doubt last night was the mounting anxiety within the Ulster Unionist Party, as two of Mr Trimble's negotiating team, Sir Reg Empey and Mr Jeffrey Donald son, warned the best efforts of the British and Irish governments could again perish on the rock of decommissioning.
British sources confirmed the eagerly awaited proposals would address "the full range" of outstanding issues - decommissioning and demilitarisation, policing reform and the future stability of the institutions of the Good Friday accord. However, they refused to be drawn on whether the proposals would be "prescriptive" or if their subsequent implementation would be in any way "conditional" on the IRA's response on the question of putting weapons beyond use.
The British government is believed ready to make significant concessions in an attempt to win at least SDLP support for the new policing dispensation in Northern Ireland. However, Sinn Fein sources appear sceptical about the possibility of the SDLP - even with Dublin support - "going it alone" on the policing issue. Unionists, meanwhile, are certain to oppose any move toward Sinn Fein demands which they consider go "beyond Patten" and would result in a potentially significant reduction in the power and accountability of the Secretary of State for Northern Ireland.