A defiant Ulster Unionist Party plunged the peace process into crisis last night with a direct challenge to the authority and prestige of the British Prime Minister, Mr Blair.
After barely 15 minutes Mr David Trimble emerged from a meeting of the UUP executive to give the clearest signal yet that he will not participate in the d'Hondt procedure, scheduled for later this morning, to appoint ministers to the North's proposed power-sharing executive.
Mr Blair was said to be "frustrated and disappointed" at Mr Trimble's verdict on his "failsafe" proposals for devolution and decommissioning.
"I have not sought, nor will I seek, a change in party policy," Mr Trimble declared, before retiring to his garden while sending Mr Blair and the Taoiseach, Mr Ahern, into crisis talks on the options now confronting them.
As reported in yesterday's Irish Times, Mr Trimble hopes to secure the agreement of London and Dublin for a review of the Belfast Agreement without any suspension of the Stormont Assembly. And the first indications early last evening were that Mr Blair might be prepared to accede to this.
On BBC television before the UUP meeting, Mr Blair had appeared resigned to rejection, expressing the belief that agreement would eventually be reached while twice raising a question mark over whether it could be done by today.
And a subsequent report, thought to have emanated from Downing Street, suggested Mr Blair's readiness to "park" the process - a proposal first mooted by Mr Trimble back in January.
But there were clear signs last night of powerful Irish Government, SDLP and Sinn Fein pressure on Mr Blair to exact a penalty of Mr Trimble if he refused to permit the creation of the executive today.
UUP members departed Glen gall Street clearly sworn to secrecy about the implications of last night's restatement of party policy. But it seemed clear the mystery surrounded questions of tactics rather than of principle.
Mr Blair and the Northern Secretary, Dr Mowlam, were consulting officials, the Irish Govern
ment and the other parties late into the night with no clear indication as to how they would respond to a second UUP rejection of the Downing Street deadline.
The Deputy First Minister-designate, Mr Seamus Mallon, is understood to be insistent that Dr Mowlam proceed as planned to trigger the d'Hondt process and carry the challenge to Mr Trimble. Whether, after a refusal by Mr Trimble to nominate ministers, the formula would be followed, resulting in a distribution of the seats between the SDLP and Sinn Fein, is unclear.
But some unionist sources have openly speculated that, in such circumstances, Mr Trimble could resign as First Minister-designate.
Against that possibility, the British government was increasingly seized of the possibility that failure to put Mr Trimble to the test might prompt Mr Mallon to resign. Since both men were elected on a joint resolution, the effect of either resigning would be to take the other with him.
Another area of feverish speculation last night concerned the position of the DUP, whose own Assembly members were meeting in emergency session at Stormont.
Some Ulster Unionist sources claimed that Dr Mowlam was determined to trigger d'Hondt and that if the DUP did nominate ministers she would actually be prepared to devolve powers to that executive. The indications were that in such an unlikely event, the UUP might actually be prepared to consider a wholesale withdrawal from the Assembly.
One official source said Mr Blair and Dr Mowlam would have to balance the need to maintain Mr Trimble's commitment to the process with the clear nationalist and republican determination that the UUP "veto" could not be a cost-free exercise.
But he refused to be drawn on the possibility that Mr Blair would ultimately grant Mr Trimble's demand to proceed to review of the agreement.
Mark Brennock, Political Correspondent, writes: The Government has insisted that the d'Hondt mechanism must be triggered today to attempt to establish the executive.
"We are gravely disappointed at what has happened," a Government spokesman said. "D'Hondt must be run."