Tony Blair has sought to win round his critics with a plea for the UN to unite against Saddam Hussein.

The prime minister said Saddam was being given "one final chance to disarm voluntarily".

To those calling for more time, Blair said: "I say we are giving it more time. But I say this too. It takes no time at all for Saddam to cooperate."

And he dismissed a memorandum from the French, German and Russian government calling for more time for the inspections process.

"They say the time is necessary 'to search out' the weapons," said Blair.

"At the core of this proposition is the notion that the task of the inspectors is to enter Iraq to find the weapons, to sniff them out as one member of the European Council put it.

"That is emphatically not the inspectors' job."

But he signalled that there would be one further pause to give the Iraqi regime a final chance to disarm.

"Today we are offering Saddam the prospect of voluntary disarmament through the UN. I detest his regime. I hope most people do. But even now he could save it by complying with the UN's demand," he told MPs.

"Even now we are prepared to go the extra step to achieve disarmament peacefully.

"I do not want war. I do not believe anyone in this House wants war.

"But disarmament peacefully can only happen with Saddam's active cooperation."

He said it was the government's "desire, and still our hope" that the UN would disarm Saddam.

"At stake in Iraq is not just peace or war. It is the authority of the UN and the international community," said Blair.

He stressed that there was "no complexity" about resolution 1441 which, he said, demanded disarmament.

His intervention followed the release of a draft UN resolution - tabled by Britain, the US and Spain - which states that Saddam is in breach of his obligations and must be disarmed.

The resolution, which will be put to a vote within a fortnight, warns that "Iraq has failed to take the final opportunity afforded to it in resolution 1441.

In his statement to MPs, the prime minister warned that Iraq is clearly flouting its UN obligations.

And he said it would be "folly" to counsel inaction given the threat the regime posed to global security.

Blair said sanctions and no-fly zones were no longer enough to contain Iraq.

Saddam is in material breach of the UN's weapons instructions, said the prime minister.

"At no stage did he cooperate as he should. At no stage did he tell the truth," he said.

The prime minister warned that the regime was intent on "internal repression and external aggression".

Tory leader Iain Duncan Smith said the onus was now on both Iraq and the UN.

"This a crucial test, not just for the US or the UK but for the United Nations," he told MPs.

"For the sake of the United Nations, and for the sake of the world, such a tyrant must be left in no doubt that if he does not disarm after years of terror and evasion he must face the consequences of his own actions."

Liberal Democrat leader Charles Kennedy said those calling for more time "offered a better route forward".

The prime minister's latest push ahead of a day-long debate on the Iraq crisis.

Dozens of Labour MPs are expected to rebel in what could become one of the bloodiest debates faced by ministers.

Between 50 and 100 MPs - including former ministers and previously loyal Blair supporters - are expected to defy a three-line whip by either abstaining or voting against the government.