Tony Blair has endured a second significant rebellion over war with Iraq but has secured a Commons majority nonetheless.

An amendment stating that the case for war had still not been made was supported by 217 MPs - 18 more than an earlier rebellion.

It is thought that up to 139 Labour MPs defied a back me or sack me threat from Tony Blair.

The scale of the rebellion was less than some had predicted - but is still the biggest of his premiership.

The main government motion - which effectively gives the green light to war - secured a two-to-one Commons majority.

The prime minister's motion won the backing of 412 MPs.

As MPs swung in behind the country's troops, fewer than 150 MPs of all parties voted against the government.

Critics say Blair must now execute a short-sharp conflict if he is to prove that war with Iraq is not a reckless adventure.

The prime minister had earlier mounted an impassioned defence of his war plans.

The last ditch appeal came as George W Bush hinted that Britain and the US could be at war within 48 hours.

Speaking in the wake of ministerial resignations and fears over the consequences of war, Blair said MPs had a duty to "give a lead" to the rest of the world.

He warned the Commons that voting against military action would only serve to strengthen other dictators. In what sounded close to a resignation threat, Blair said that he would "not be a party to such a course".

Blair said that the Iraqi regime had pushed the international community "to the limit".

"To fall back into the latitude of the last 12 years, to discuss, to debate but never to act. To declare our will but not to enforce it, to continue with strong language but weak intentions - that is the worst course imaginable," he said.

The Labour leader later worked the Commons in a bid to meet and greet MPs who have expressed misgivings about a military conflict.

Clare Short's decision to stay within the Cabinet was seen as early evidence that the prime minister was winning the day.

She said resignation would have been the easy way out - but continued to stress she was "very critical" of the handling of the crisis.

"I know I will be heavily criticised for this decision, but we must all do what we think is right in the circumstances we are now in," she said.

Blair also secured the support of the Conservative Party leader Iain Duncan Smith.

"This is in the British national interest. Saddam Hussein has the means, the mentality and the motive to pose a direct threat to our national security," he told MPs.

"That is why we will be voting tonight to do the right thing by our troops and our national security."

William Hague also mounted a passionate defence of the prime minister's stance.

Reflecting on the US's image as the world's policeman he said America "takes on that role because others shirk it."

"It is necessary that those who wish to be rogue states know what happens to those that are," said Hague.

"Not to take action now is to reduce the credibility of any action. The time has come for a decision."

But the vocal band of anti-war MPs stood their ground despite the imminence of British engagement in war.

Former defence minister Peter Kilfoyle told the Commons that a conflict would be "illegal, immoral and illogical".

Kilfoyle warned that war against Saddam would "reap a whirlwind which will affect us for generations to come".

As opinion polls showed that support for war was growing in the country at large opponents of military action moved to reduce the political consequences of their stance.

Under heavy fire in the Commons, Charles Kennedy said there was "no contradiction" between giving voice to legitimate anxiety and at the same time giving "full moral support to our forces".

"Before launching an almighty assault upon Iraq, are we not better to pursue the cause of disarmament on the ground in the presence of weapons inspectors?" he asked.

The SNP's defence spokesman Angus Robertson said his party would give its support to Britain's forces when war is announced.

In a letter to troops and their families he said: "There is a world of difference between expressing solidarity with our service community and giving Tony Blair and George W Bush a blank cheque for unilateral military conflict."

Labour's Graham Allen said the prime minister should "take urgent steps to reunite himself with his party and with parliament" following the rebellion.

"Unrestrained executive power may have reached its zenith, with the prime minister overextending himself in the assurances he gave to the US president.

"Recent events must bring closer the day when prime ministerial power in the UK is defined, legalised, and checked," he said.