After eight hours of impassioned debate in the House of Commons last night, the Northern Ireland Bill including the controversial failsafe mechanism, was passed by 343 votes to 24.
The UUP leader, Mr David Trimble, abstained but five Ulster Unionist MPs voted against the government, as did the Democratic Unionist leader, the Rev Ian Paisley, his deputy, Mr Peter Robinson, the UK Unionist Mr Robert McCartney and 16 Tory MPs including the former Home Secretary Michael Howard.
The rest of the Conservatives abstained, underlining the breach of the traditional bi-partisan approach by the main parties on Northern Ireland issues.
The Bill is expected to clear the House of Lords by tomorrow. However, Mr Blair's goal of achieving a transfer of power in Northern Ireland to a devolved, power-sharing executive by Sunday was thrown into doubt by Mr Trimble's attack on the legislation.
The Northern Ireland First Minister designate told MPs the fail-safe measures, supposed to ensure that Sinn Fein could not carry on in government if the IRA did not disarm, were "flawed and unfair".
Earlier, the House of Commons had given the Bill its second reading by 312 votes to 19, a government majority of 293 in a division forced by Ulster Unionists.
Ten Tories joined the UUP, DUP and UK Unionists in voting against the Bill's second reading.
Introducing the Bill, the Northern Secretary, Dr Mo Mowlam, urged opponents of emergency legislation to stabilise the Ulster peace process "to take a risk" and trust that decommissioning would happen. She described the Bill as the "best chance" for getting the decommissioning process started.
The Bill was being rushed through all its Commons stages in just one sitting last night despite criticism from the Rev Ian Paisley, that the time was insufficient for such an important measure.
Under the Bill, if commitments are breached by either side on decommissioning or on devolving the institutions set up by the Belfast Agreement, the institutions will be suspended. Northern Ireland would be returned to direct rule with the executive brought to an end.
The precise timetable of decommissioning of paramilitary arms has been left to an independent decommissioning body headed by Gen John de Chastelain. Dr Mowlam said he had made it clear "there will be a process of decommissioning within days of the devolution and there will be, within weeks, the first act of decommissioning".
To Tory shouts of "how long?", Dr Mowlam said: "What we have here is the best chance, the best option, for not just getting a token gesture of decommissioning, but for a process, starting now, finishing and completed by May 2000.
"Any suggestion in the past has been a token gesture. Why this I believe is the best option we have ever had to make real peace in Northern Ireland is it will be a timetable for complete decommissioning by May 2000."
She declared: "That I believe is worth taking a risk and it is, I accept, partially a risk. It is partially a risk because what it does is say that after d'Hondt on Thursday, after devolution on Saturday, it will be a matter of days before the process starts and weeks before actual decommissioning starts. Now is that too long to wait to see if this process can work?"
The Prime Minister was on the front bench as Dr Mowlam opened the debate.
Dr Mowlam said the Bill would provide automatic and immediate suspension of the operation of the institutions established under the Belfast Agreement if either decommissioning or devolution commitments were not met.
"The effect of suspension is that the Northern Ireland Assembly will no longer be able to legislate or to meet apart from specific circumstances for which the Bill provides," she said. "Ministers will cease to hold office. The North-South ministerial council and the British-Irish council will cease to function under the terms of a supplementary treaty between the two governments." All legislative and executive functions during the suspension period would revert to Westminster.
The Ulster Unionist leader, Mr Trimble, asked if a failure by one side to co-operate with the commission would affect early release of prisoners under the Belfast Agreement. "Can you not say that the remedy with regard to prisoners will be just as swift and just as certain as the remedy that is provided for under this Bill?"
Dr Mowlam said: "I can't rewrite the agreement, as you know. There is a clear relationship between prisoner releases and ceasefire. There is not that relationship between accelerated release for prisoners and decommissioning."
Mr Trimble said the Prime Minister knew his party was "reluctant" to take part in an executive with Sinn Fein in advance of decommissioning. "Our reluctance will be portrayed by some as an unwillingness to share in an administration with Catholics or nationalists. This is untrue."
Mr Trimble said his party did not even have an "absolute objection" to sitting down with past terrorists.
"Our problem isn't with former terrorists. It's about taking an existing and active terrorist organisation into government. He condemned the so-called "failsafes" as "flawed and unfair". It was unfair because if Sinn Fein broke its obligations, then everyone in the executive was ejected from office. "The innocent are punished along with the guilty and the democrats are treated as if they were indistinguishable from the terrorists.
"The fair response is that the offending party should be removed." If that was in the Bill it would go a long way to making it acceptable. But it was not. Mr Trimble said another flaw was that the decommissioning scheme was not set down in a precise timetable.
Ulster Unionist Mr Jeffrey Donaldson said he believed the British public was changing its opinion on prisoner releases, especially after the release of Brighton bomber Patrick Magee. He said the pressure to believe the IRA had given up violence was accompanied by the threat that if his party did not, terrorism would prevail.
The SDLP leader, Mr John Hume, acknowledged the "enormous progress" made in Northern Ireland. "The atmosphere on the streets had been transformed and young people who had only ever known violence were more aware than anyone of that progress."
"The most important thing that has happened is that the final word in the Good Friday agreement was not with the politicians, it was with the people. "This was quite historic in the sense that, for the first time in our history, the people of Ireland, North and South, spoke as to how they wished to share the peace of Ireland together."
He added that there had been a transformation in Nationalist thinking across Ireland because agreement was now seen as the only way of solving division.
The SDLP leader appealed to Tories not to treat the issue of Northern Ireland as one of party politics.
He suggested Mr Hague should meet the SDLP in order to keep abreast of all opinions in Northern Ireland. "Never yet have we had a meeting with your leadership since it took over and what does that tell you about the real interest in our situation?"
The Northern Ireland Deputy First Minister, Mr Seamus Mallon, backed the Bill but opposed that part of it which, he said, departed from the Belfast Agreement. "This is legislation which I sincerely hope will never be used," he told MPs.
"Indeed it's a sad commentary on the situation we are in - and I mean all of us, those who live in Northern Ireland and those who legislate for Northern Ireland - that, at a time when people are about to enter partnership, what they want to know is how they will deal with the demise of that partnership."
He continued: "Maybe it's an Irish thing or maybe the Irish thing has permeated into British legislation, but it's almost as if before the wedding is consummated, the funeral cortege is arranged for either the bride or the bridegroom." It was "legislation for what-ifs", Mr Mallon declared, a "charter for mistrust".
He said it would have been better if legislation had been introduced "when it was clear" there was justification for that mistrust. The legislation had been brought forward to satisfy unionist demands over the failsafe mechanism, he said. "We are seeking to put in place new arrangements for failure before we are even begin a journey which might bring us success."
Mr Mallon warned the unionists: "I can assure you of this, if any party associated with the paramilitaries breaks his word to the people of Ireland in terms of the commitment given in The Way Forward document, we will not be ignoring them. We will not be shirking from the consideration of penalty as we will not shirk from the consideration of penalty if and indeed it is broken by any of the unionist parties."
Dr Paisley said he wanted the Bill modified so that if a party connected to paramilitaries was in default, not only should the release of its prisoners be halted, the ones already out should be incarcerated again.
The former Prime Minister, Mr John Major, described it as "perverse" that the Ulster Unionists were being asked to take one more risk for peace on the good faith of the IRA. However, Mr Major, who initiated the peace process when in office, said governments had been forced to deal with "unsavoury characters" in the past in the quest for peace.
Mr Major questioned Sinn Fein's link to the IRA: "If Sinn Fein have no influence with the IRA then Sinn Fein are but a tiny political group of much less importance than those represented in this House.
"But if they do have influence with the IRA then let us realise with whom democracy will be sitting down with in the power-sharing executive when they take their seats there." That is why Sinn Fein must be expelled if the IRA failed to disarm, he said.
Replying to the debate, Northern Ireland Minister of State Mr Paul Murphy stressed Gen de Chastelain had laid down an "indicative timetable" for decommissioning. Mr Murphy assured Mr Trimble his party would not come under pressure from the government to overlook any breaches of the decommissioning process and move forward in an unchanged executive.
"The people of Northern Ireland are looking to us here in this chamber, but also to the parties in Northern Ireland, to settle this particular impasse, to break the deadlock. Unless we find that there are better ideas, then I think that the best chance that we have of ensuring first of all that devolution occurs and also that decommissioning occurs is precisely what is embedded in this Bill."
He said the relationship between British and Irish governments "has never been closer"
Later, in the Bill's line-by-line committee stage debate, a Tory call for early terrorist prisoner releases to be halted if any paramilitary groups defaulted on decommissioning was defeated by 349 votes to 147 - a government majority of 202.