Tony Blair last night fought off a backbench rebellion as fewer than expected MPs voted against military action.

With 139 MPs voting for an amendment to a Government motion authorising the use of force, Downing Street appeared relieved that predicted higher figures failed to materialise.

Downing Street brushed off the 18 more MPs who voted with the rebels from last time there was a debate on Iraq, claiming they were fulfilling promises to local constituency parties.

The Government had promised the debate and vote on a substantive motion as a precondition for sending in troops into Iraq. After last night, the final political obstacle has been cleared.

What was the final day of Parliamentary debate about the rights and wrongs of starting war began with Mr Blair rocked by Home Office Minister John Denham and Health Minister Lord Hunt, joining Robin Cook in leaving Government.

In a final twist to her resignation saga, Clare Short decided to hold on to her job as International Development Secretary, despite her previous threats to quit.

The Tories too faced divisions with shadow environment minister Jonathan Sayeed, shadow home affairs minister Humfrey Malins, and shadow health minister John Baron all resigning from the front bench team.

At about 12.30, the Mr Blair rose to make a passionate one-hour speech to a packed House of Commons, presenting his case for sending British troops in Iraq.

Seeming to shake off the haggard look of recent weeks, he said future wars would be "much worse and more devastating" unless action was taken against Saddam Hussein now.

"Our fault has not been impatience," he said. "The truth is that our patience should have been exhausted weeks and months years ago."

While the Prime Minister said there have been "glib and foolish" comparisons with the 1930s and that "no one here is an appeaser" he nonetheless went on to draw parallels between the present situation and the League of Nations failure to stand up to Hitler.

"I have come to the conclusion after much reluctance that the greater danger to the UN is inaction - that to pass Resolution 1441 and then refuse to enforce it would do the most deadly damage to the UN's future strength."

In a final swipe at the French he said if President Jacques Chirac had not threatened to veto a new UN resolution setting a deadline for Saddam to disarm, he may have backed down without the use of force.

"The tragedy is that, had such a resolution been issued, he might just have complied," Mr Blair said.

With one eye on the raw numbers game that will determine his political future, Mr Blair made one final plea to MPs who might have been wavering.

"If this House now demands that at this moment, faced with this threat from this regime, that British troops are pulled back, that we turn away at the point of reckoning - and that is what it means - what then?" he said.

"What will Saddam feel? Strengthened beyond measure. What will the other states who tyrannise their people, the terrorists who threaten our existence, what will they take from that? That the will confronting them is decaying and feeble.

"This is not the time to falter. It is time for this House to give a lead, to show that we will stand up for what we know to be right."

But Mr Denham said it was American "disdain" for international opinion which had led to the failure to agree a new resolution, and warned of the dangers of acting without UN support.

"If I believed it would work, I could swallow my qualms. But I don't," he said.

"I believe the reaction to this way of working will be as dangerous as the problems we are trying to solve - turning many parts of the world against us, undermining friendly governments, fuelling terrorism and those who will join it in the future, making it more difficult to sustain international action against common problems."

Meanwhile, the decision of Britain and the US to press ahead with military force continued to divide the international community.

President Chirac said Iraq did not represent "an immediate threat that would justify an immediate war" while Russian Foreign Minister Igor Ivanov said military action would jeopardise "the international anti-terror coalition".

US Secretary of State Colin Powell countered by claiming the support of 30 nations in a "coalition of the willing" to bring down Saddam Hussein, with another 15 having quietly promised their support.

White House spokesman Ari Fleischer dismissed the Baghdad regime's rejection of President Bush's ultimatum.

"This is the latest mistake Iraq could make. It would be Saddam's final mistake," he said.

He refused to rule out an attack before the ultimatum runs out at 1am GMT on Thursday morning