The Ulster Unionist leader and his deputy John Taylor abstained during the final vote on the Northern Ireland Bill although they earlier voted against the legislation's second reading.
It was unclear last night why Mr Trimble withdrew his opposition but his decision will be seen by his supporters as a significant signal in the peace process.
The Bill now goes to the Lords for two days of debate in a bid to meet the Prime Minister's goal of achieving a transfer of power to a devolved, power-sharing Northern Ireland executive by Sunday.
Mr Trimble may have responded to an appeal to his Ulster Unionist Party (UUP) executive from Mo Mowlam to "take a risk for peace." Launching the Bill in the House of Commons, the Northern Ireland secretary also offered assurances on the future of the controversial prisoner-release programme in an attempt to keep the Northern Ireland peace process from collapse.
Mr Trimble's late night move came came despite his earlier attack on the Government's "failsafe" guarantee for IRA disarmament. Mr Trimble, the First Minister of Northern Ireland, said the mechanism drawn up to ensure Sinn Fein would not be able to sit in a new power-sharing executive if the IRA did not hand in its weapons was "flawed and unfair".
The Bill could remain on the statute book to be enacted when an agreement is reached, but if the Unionists refuse tomorrow to nominate their team to serve with Sinn Fein on the executive, the British and Irish governments will have to return to the drawing board. Sources at Westminster were refusing to rule out the possibility of a second referendum in Northern Ireland to appeal over the heads of the UUP leaders.
Mr Trimble, who is under pressure from his own party not to give too much ground to Sinn Fein, appealed for more time from the Government. It is possible he will try to avoid the Ulster Unionists being blamed for taking the peace process to the brink of collapse by declining to issue a clear-cut rejection when he addresses the UUP ruling executive in Belfast today .
The Ulster Unionists had joined the Conservatives in a vain attempt to force through greater safeguards in the Northern Ireland Bill - to provide a legislative timetable for decommissioning, an automatic power to expel Sinn Fein from the power-sharing executive if the IRA failed to make progress within weeks on decommissioning, and a halt to prisoner releases if Sinn Fein defaulted on its commitments to the Good Friday Agreement.
The Government refused to accept the amendments, but Ms Mowlam made clear that if the independent commissioner on decommissioning, General John de Chastelain, found that the IRA had failed to start destroying its weapons "within weeks", the Northern Ireland Assembly would have a vote to expel Sinn Fein. And on prisoner releases, she gave Mr Trimble the assurance that she would have to take into account whether the ceasefires were holding before allowing releases to continue.
A government source said: "We can't go beyond what is in the Good Friday Agreement. If we did we would lose Sinn Fein."
Downing Street later said it was "looking closely" at a call by the former prime minister John Major, given during the debate, for the publication of details of the destruction of weapons should the IRA agree to disarm. He also asked the SDLP to give an assurance that it would remain in the executive should Sinn Fein be expelled.
Meanwhile, republicans in Belfast were making clear that they disliked the thrust of the proposed legislation which, they claimed, was outside the terms of the Agreement. They claimed that the Unionists were suffering from "reluctance and paranoia" and that Tony Blair was conceding too much in an effort to assuage their concerns.
There are worries within the republicans' support base that Sinn Fein and the IRA might be giving too much away on decommissioning, although the doubts in those quarters seem to amount to much less of a problem than those being experienced within Unionism.
The Taoiseach, Bertie Ahern,said that to turn down the deal would be "a mistake of historic proportions".Reuse content