The Bill was given an overwhelming second reading in the Commons by 343 votes to 10, but its rejection by Mr Trimble, who has been praised for his courageous support for the peace proposals, came as a blow for Mo Mowlam, the Northern Ireland Secretary.
The Ulster Unionist leader had signalled in the days leading up to the second reading that he was content for the Northern Ireland (Sentences) Bill to be put on to the Statute Book after the assurances given by the Prime Minister that prisoner releases would be linked to decommissioning of weapons by terrorist groups.
But the Ulster Unionist MPs were dismayed by the failure of Adam Ingram, the minister for Northern Ireland, to satisfy them in his wind-up speech minutes before the vote about the linkage, and they marched into the "no" lobby with the backing of three Tory MPs - Nicholas Winterton, Laurence Robertson, and Howard Flight - and the Democratic Unionist MPs, led by Ian Paisley.
One Unionist MP said: "Trimble realises it was a vote for self-preservation. He is out of step with the rest of his party at Westminster, and he has come up with the right response."
Robert McCartney (UKUP Down North) denied those opposing the Bill were "wreckers" and opponents of peace. "I oppose the agreement and I oppose this Bill because I desire peace," he said.
The Northern Ireland Secretary, who faced sniping from the Opposition party benches over the alleged failure to link early prisoner releases with the decommissioning of arms, now faces a series of amendments in the Bill's committee stage next week.
Some of the Unionists were threatening to table an amendment demanding more compensation for the victims of violence. There will be attempts to write into the legislation a more explicit commitment that no prisoners will be released until guns and bombs have been decommissioned.
Andrew Mackay, the Tory spokesman on Ulster, warned Ms Mowlam that the Opposition would not co-operate with a "fast track" procedure to rush the Bill on to the Statute Book without close scrutiny in the committee stage. However, Ms Mowlam stood firm, saying the legislation was not to be "cherry picked by any party".
Under the Good Friday agreement, the Secretary of State has the power to veto releases recommended by an independent body, if she is not satisfied that they have given up violence for good.
Ms Mowlam insisted that the safeguards to ensure that freed terrorists had renounced violence were rigorous. And she denied she was preparing to make the IRA legal. Membership of such organisations would continue to be a criminal offence.
Mr Trimble said the substance of the agreement had been watered down in the proposed legislation. He said the Government must stick very closely to the conditions for early prisoner release.Reuse content