Can the Sinn Fein president, Mr Gerry Adams, persuade the IRA to commence decommissioning and avert Mr David Trimble's resignation as First Minister? And can the Belfast Agreement survive the loss of the Ulster Unionist leader?

These were among the questions exercising the Taoiseach, Mr Ahern, and the British Prime Minister, Mr Tony Blair, at Downing Street yesterday afternoon as they took the post-election mood and set the scene for yet another make-or-break negotiation for Northern Ireland next week.

At this writing, the answer to the first question appears to be that they quite simply don't know. The answer to the second is probably a highly reluctant "yes", or at any rate, "possibly".

Certainly, that appears to be the determined message from the Northern Secretary, Dr John Reid. "There Is No Alternative," he intones with the stubborn steeliness of a latter-day Thatcher. No re-casting. No re-negotiation. "What we have we hold," he might have added, in language the average unionist would readily comprehend.

Many of them will bridle at this. On the BBC's On The Record programme on Sunday Dr Reid conceded that a majority of unionists had voted for declared opponents of the Good Friday accord. Carried to its seemingly logical conclusion that would appear to threaten nothing less than a full-blown crisis of democracy.

Many years ago Mr John Hume established in London's mind that "majoritarianism" was not a sufficient basis for the governance of Northern Ireland. Having brought the unionist parties (including the DUP) reluctantly to accept this reality, the Belfast Agreement was consequently rooted in the principle of dual consent by both the unionist and nationalist communities.

If the SDLP or Sinn Fein withdrew from Stormont - say over policing or demilitarisation - Dr Reid would hardly insist the agreement proceed without them. Likewise, if the unionist community's consent to the present dispensation was explicitly withdrawn, the Secretary of State's avowal that there is no alternative might begin to ring rather hollow. Consent, as Mr Hume might say, is a two-way street.

However, Dr Reid's contention - correct, at least for the moment - was that the unionist position was a good deal more complex than it might appear from a quick scan of the general and district council election results.

Indeed, his advisers may feel this is Mr Trimble's strongest suit as he prepares for Saturday's meeting of the Ulster Unionist Council. Whatever about the seats he has lost, Mr Trimble will certainly calculate that he has won - or is in the process of winning - the internal unionist argument.

Mr Trimble went to Downing Street last week to urge Mr Blair to "recalibrate" his Northern Ireland policy in favour of the centre parties. However, some think the most conspicuous recalibration of policy lately has been that effected by the Democratic Unionists.

On the Sunday after the Westminster election, the newly elected and highly talented MP for North Belfast, Mr Nigel Dodds, appeared on the BBC's Breakfast with Frost programme. Anybody who had missed the introduction, and didn't know who Mr Dodds was, might have been forgiven for thinking they were listening to a sceptical but still-wanting-to-be-persuaded member of the UUP. The DUP was in favour of devolution, he insisted; it wanted Sinn Fein to prove its democratic bona fides, and was simply determined that promises made on decommissioning must be kept.

Had he been watching, it is unlikely Mr Trimble would have found much with which to disagree. And he would have glowed contentedly as Sir David Frost observed - it seemed to his own surprise - that Mr Trimble's was the only post-dated resignation letter currently with the Assembly's presiding officer.

Sir David was pointing up the lack of clarity as to whether - if there is no decommissioning by July 1st and Mr Trimble resigns as First Minister - the DUP's "ministers-in-opposition" will follow suit.

There is no doubt the British government does not want to lose Mr Trimble. The Prime Minister plainly rates his First Minister head-and-shoulders above any of his putative successors, and would find it incredible that unionists might so wish.

But if they do? There would, for sure, be uncertainty in Downing Street, and dread of protracted delay as unionism in that event realigned and redefined itself. However, the calculation would be that a new unionist leadership's mission would emphatically be not to lose the devolved Assembly.

This would appear to be Mr Trimble's second advantage ahead of Saturday. His long-term tenure as leader looks suddenly more shaky. He has undoubtedly taken some serious hits, and there is an apparent seepage of confidence among some senior pro-agreement supporters. However, those advocating the Donald son/Empey "dream ticket" are not doing so with a view to collapsing the Assembly. On the contrary, some of them argue that a new leader might be better placed to resolve outstanding problems because he would be inheriting a situation not of his making.

Whether that would prove to be so, Mr Trimble's third case against a leadership challenge on Saturday will be that the delegates may not have to wait long to see the argument tested. Mr Donaldson's inclusion on his talks team yesterday would seem designed to dispel any doubt that Mr Trimble is serious about the July 1st deadline. That would give the two governments at least until mid-August to try to square the decommissioning-demilitarisation-policing-institutional circle. But if Mr Trimble walks on July 1st he will hardly return without decommissioning - if only because he does not have the Assembly votes to guarantee re-election.

The nagging fear in London and Dublin is that the republicans might actually wish to see Mr Trimble fall and the unionists further splinter and divide. Against that is the seemingly compelling evidence that Mr Adams's political project has proved a winner - and that a self-partitioning, mutually excluding Northern Ireland is hardly compatible with Sinn Fein's own declared destination.

Asked yesterday if he was optimistic, one British source preferred "realistic" as he pondered the prospects for a breakthrough. But Mr Blair and Mr Ahern will still be travelling hopefully. It is in the resilient way of Anglo-Irish diplomacy to see that, while the elections have caused problems for Mr Trimble, Sinn Fein's success has also opened a window of opportunity.