Tony Blair has set out the key tests that could form the basis of a second United Nations resolution authorising war with Iraq.

Facing sceptical questioning from all sides of the Commons, the prime minister urged the international community to back the compromise move currently being discussed in New York.

He revealed that the resolution would demand that Iraq account for anthrax stocks and permit scientists and their families to leave the country to be interviewed by weapons inspectors.

The regime must also provide more information on unmanned aerial vehicles that could be used to distribute weapons of mass destruction, the Commons heard.

And there should also be a commitment to destroying mobile biological warfare production units and banned missiles.

Foreign secretary Jack Straw had earlier called on Saddam Hussein to take to the Iraqi airwaves to confess his ownership of weapons of mass destruction.

The debate on a second resolution would be pushed forward "in a way that most upholds the authority of the UN", Blair promised MPs.

But he repeatedly refused to rule out going to war without a second resolution - an indication that the British government expects French president Jacques Chirac to veto military action.

The prime minister warned that the worst outcome would be to allow Saddam Hussein to flout the will of the security council.

"What we must show is the determination to act if Saddam will not fully comply," he said.

"I will certainly do everything that I can to ensure that the international community stays united at this time."

However the prime minister was forced on to the defensive by comments from Donald Rumsfeld - who said that America could act without UK military support.

Number 10 said British troops would play "a significant part" in any war.

Speaking in the Commons, opposition leader Iain Duncan Smith asked if America would go to war without the UK.

Tony Blair said it was true that the United States "could go it alone".

But he added that his backing for military action was based on the British national interest which had to be "upheld at all times".

The international community should "back up the clear instruction" that Saddam must disarm, said Blair.

"That is why I am determined that we hold firm to the course that we have set out," he said.

Pressed on Clare Short's criticism of his "reckless" actions, Blair insisted that collective cabinet responsibility still applied.

The Conservative leader, however, said Short could not remain in cabinet following her attack.

"If he can't convince his own cabinet it is going to be very difficult to convince the British people," Duncan Smith warned.

Blair said it was better to discuss "the substance" of the issue.

But he later added that he could not rely on support from his own administration "from time to time".

Liberal Democrat leader Charles Kennedy challenged the prime minister on the legality of America going it alone without a UN mandate.

He asked what advice the attorney general had offered.

"We would not do anything as a country that does not have a proper legal basis," said Blair.

Kennedy was unconvinced, highlighting the UN secretary general's warning that military action could breach its charter.

"Is Kofi Annan wrong?" he asked.

Blair called for support for his campaign to get agreement in the UN and then turned his fire on Russia's pledge to veto the second resolution.

"It is complicated enough to get that agreement when one country is saying that whatever the circumstances it would veto any resolution," said the prime minister.