Gordon Brown won a hollow victory for his new 42-day anti-terrorism powers last night when he was forced to rely on the votes of nine Democratic Unionist Party MPs during a day of backroom deals and concessions.
Although plans to detain suspected terrorists for up to 42 days were approved by 315 votes to 306, Labour MPs described the outcome as "the worst of all worlds" and said Mr Brown's decision to stake his reputation on the vote had backfired badly.
A bad day for Mr Brown got even worse when it emerged that highly-classified documents about the scale of the threat from al-Qa'ida were left on a train by a Whitehall official. It was the most serious in an embarrassing spate of sensitive data losses which have bedevilled the Brown Government.
Amid renewed doubts among his own MPs about whether Mr Brown should lead his party into the general election, ministers privately expressed fears that the 42-day detention plan could yet be defeated in Parliament.
The House of Lords looks certain to throw out the proposal overwhelmingly and ministers fear the narrowness of last night's vote will embolden more Labour rebels to vote against the Counter-Terrorism Bill should it return to the Commons. Thirty-six Labour MPs opposed it last night but organisers claim another 25 have grave reservations.
Downing Street insisted there had been no backstairs deal with the DUP. But rumours swept Westminster that the party which normally votes with the Tories had been bought off by promises of £100m of infrastucture projects in Northern Ireland and that the province would keep revenues from water charges rather than hand them over to the Treasury.
Labour critics of Mr Brown said his handling of the Bill had raised further doubts about his future as Prime Minister – and that an attempt to look tough on security had been neutered by the concessions he made in order to win over Labour rebels. One former minister said: "This was a crisis of Gordon's own making. He wanted to show strength but ended up showing profound weakness."
Some MPs warned that Mr Brown had "one last chance" to revive his premiership and would need to show real momentum by the party conference in Manchester in September to be sure of leading Labour into the next election. If he faltered, opponents predicted, a delegation of senior cabinet ministers would ask him to stand down for the sake of the party.
Despite relief at avoiding his first Commons defeat, Mr Brown will be brought down to earth today when he attends a Labour Party inquest into the party's disastrous performance at the local elections and Crewe and Nantwich by-election. He will also face a backlash over the missing security document.
The Conservatives and Liberal Democrats were swift to capitalise on the loss, which they said underlined the Government's incompetence.
Baroness Neville-Jones, the Conservative security spokeswoman, said: "This is just the latest in a long line of serious breaches of security involving either the loss of data, documents or government laptops, further highlighting the most basic failures in this government's ability to maintain our security. The Government must make an immediate statement to Parliament and an inquiry must be launched."
Chris Huhne, the Liberal Democrat home affairs spokesman, said: "This is an appalling breach of security, which suggests that procedures on such sensitive matters are lax to the point of utter carelessness. There should be strict guidelines about when such secret documents are outside carefully monitored premises. It beggars belief that the Government could have scored such a devastating own goal on the very day that it was pushing draconian counter-terrorism laws through Parliament."
At a meeting of Labour's ruling National Executive Committee (NEC), Mr Brown will hear criticism of his decision to abolish the 10p rate of income tax. "This alienated Labour's activists and core voters, those directly affected and those who think it is morally wrong," says a motion submitted by NEC members Ann Black and Pete Willsman.
They demand full compensation for the one million low-paid workers not helped by the £2.7bn package announced last month, and for the one-off payments for this year to be extended.
At a press conference today, the Prime Minister will promise to switch his focus on to people's concerns about the economy after the 42-day victory. "A win is a win," one relieved aide said.
"We won the argument; they bought the vote," said David Davis, the shadow Home Secretary. He said 42-day detention had "no parliamentary authority".
The Rev William McCrae, a DUP MP, insisted his party's move was not a matter of "propping up" the Prime Minister. "We decided on an issue of principle, on national security," he said.
A long power struggle between the Commons and the Lords could drag on beyond the current session of Parliament ending this autumn. John Grogan, one of the Labour rebels, said: "This is the worst possible revolt for the Government." He added: "The issue will dominate politics for the next 18 months. If it loses in the Lords, it should think again."
Bob Marshall-Andrews, another rebel, said: "Gordon Brown won the vote on the back of the Irish vote – nine Irish votes. That is going to play very, very badly in the country."
But Tony McNulty, the Home Office minister, said it would be "perverse" to interpret the vote as damaging to Mr Brown. He asked: "How on earth can the Prime Minister's stock be damaged if he has done what the country needs and desires, what our police want in terms of protection of the people of this country against the terrorist threat?"