Last night Mr David Trimble appeared set for the biggest gamble of his political life. Decide between me and Jeffrey Donaldson, was his implicit message to the 860 members of Ulster Unionist Council. The tussle has now got personal.

The First Minister was faced with the most daunting of decisions: to do a deal with Mr Donaldson or confront him at the Waterfront Hall, Belfast tomorrow. That translates as a battle for the heart and soul of the Ulster Unionist Party, for Mr Trimble's political future and for that of the Belfast Agreement.

For much of yesterday, judging by comments from some of his close colleagues and aides, Mr Trimble swayed between forging a deal with the Lagan Valley MP and attempting to face him down tomorrow. At teatime he appeared to choose the latter option.

Around 5 p.m. Mr Trimble met Tony Blair at Stormont while two of his envoys, Assembly members Danny Kennedy and Fred Cobain, were holding talks with Mr Donaldson, seeking to establish if middle ground could be found between the Yes and No positions.

Sources close to Mr Donaldson said the contact with the MLAs throughout the day was gradually bearing fruit. Mr Donaldson had tabled a motion setting a decommissioning deadline for the end of November, but no actual withdrawal from the Executive until Christmas.

Mr Donaldson felt, and it seems Mr Kennedy and Mr Cobain agreed, that a compromise motion could be forged, possibly setting a deadline in the new year. Mr Cobain and Mr Kennedy also asked Mr Donaldson if he was prepared to fine-tune his motion where the party would withdraw immediately from the North-South bodies, arrange a review of the workings of the Belfast Agreement and demand a moratorium on the implementation of Patten.

Whatever strategy might be adopted, some sort of deal appeared to be within their grasp.

However, what annoyed Mr Donaldson was a statement from UUP Minister Michael McGimpsey earlier in the day that was dismissive of the No motion and Mr Donaldson.

Mr Donaldson, according to reliable sources, believed this was not Mr Trimble's view. At teatime he was proved wrong. Before his meeting with Mr Blair, the First Minister had the demeanour of a politician agonising over difficult decisions. Whatever discussion took place between the two of them at Castle Buildings he was a different man after the encounter.

He lit the fuse. This was his view of the Donaldson motion: "I saw the letter that has been sent out. I think Michael [McGimpsey] described it extremely accurately as Jeffrey's letter to Santa. It has the same connection with the real world.

"It looks to me as though the proposals that were sent out have sunk the discussions that were ongoing," added Mr Trimble.

And just to emphasise that the distance between their two positions was wide and widening, Mr Trimble stressed that while he was prepared to impose phased sanctions if the IRA were not more forthcoming on arms, he implied deadlines were not the way forward.

"The problem with a deadline is that it is telling the republicans how they escape from pressure," said Mr Trimble. "Jeffrey wants to set a deadline in five weeks' time. That is telling republicans all they have got to do is hunker down and withstand the pressure for five weeks, and then bingo, they will have escaped because the unionists have run away.

"And they can blame the unionists for setting the deadline and walking away. That sort of crude device is counter-productive. There is more than one way to skin a cat."

Mr Donaldson, the Lagan Valley MP, is understood to have been shocked by the tone of Mr Trimble's comments. Mr Cobain and Mr Kennedy were said to be disillusioned. Even some of Mr Trimble's trusted colleagues appeared taken aback. Sir Reg Empey, standing beside the First Minister at the press conference, offered an olive branch to the No camp.

"I hope and pray that over the next 48 hours we will find an accommodation, and it won't be for the want of trying," Sir Reg said.

Later last night, Mr Trimble, on BBC's Hearts and Minds programme, said of course he would be delighted if a compromise motion might yet be agreed by tomorrow. This may have been said tongue in cheek, because then he stuck the blade deeper into Mr Donaldson. His motion was "fatally flawed", said Mr Trimble.

Mr Trimble's comments were a classic "back-me-or-sack-me" challenge. There are still 24 hours to go and who can say that a compromise motion might not yet be agreed. But were Mr Donaldson to sign up to a motion anywhere along the lines of Mr Trimble's current thinking it would be perceived as surrender.

Still, the outcome of the Ulster Unionist Council meeting remains difficult to determine, because there are several factors that could shift the balance.

As at previous unionist shootouts, a crucial question is over which way John Taylor will side.

A straight contest between Mr Trimble and Mr Donaldson could go either way, but if the anti-agreement strategists achieve their policy of divide and conquer by turning the Strangford MP, and/or some of the hitherto loyal Trimble UUP Assembly members such as an irked Mr Kennedy and Mr Cobain, then it would be more difficult for the First Minister and for the Belfast Agreement.

If his current allies stick with him he has a reasonable chance. And last night Mr Trimble was confident that Mr Taylor would side with him tomorrow, although nobody is taking bets on what the unpredictable Mr Taylor will do.

This makes for exciting politics. Tomorrow's outcome will depend on how wavering council members respond to Mr Trimble's bold gamble.

Mr Trimble appeared sufficiently confident to tell the BBC's Seamus McKee last night: "I am afraid you are going to get stuck with me a little longer."