Tony Blair still intends to show "a determination to act" against Iraq despite a welter of criticism from his own MPs.

With British troops preparing for military action, the prime minister wanted to "send the strongest possible signal" that he will act.

To those calling for more time, Blair said leaving British troops sitting on the border as Iraq continued to defy the UN's will would "send a message of weakness not just to Saddam but across the world".

And even today, as the US flexes it muscles in the skies above Iraq, war is not inevitable, Blair insisted.

"I believe that if we set those conditions out clearly, if we back them by the will of a united UN, then we have a chance even now of averting conflict," the Commons was told.

The cabinet sat alongside the prime minister as he faced one of his toughest questions sessions since assuming office.

But Clare Short, whose intervention sparked the latest crisis in his leadership, was conspicuously absent.

Her supporters, however, were there in spades: and pointed out to the prime minister that it would not be a war in their name.

The first MP up was Peter Bradley, a Labour loyalist, who warned against "precipitive action".

Barry Sheerman said the prime minister had to tell president Bush that a second resolution had to be achieved before he could proceed with war.

Fending off critics on his own side, Tony Blair insisted that a decision to go to war would be taken "in the British national interest".

Even opposition leader Iain Duncan Smith, who backs Blair's coalition of the willing, wasn't entirely on side.

Quoting Short's remarks, he asked whether the prime minister's "tent was big enough" to house both the international development secretary and US defence secretary Donald Rumsfeld.

And what had happened to the convention that the Cabinet speaks with one voice, asked Duncan Smith quizzically?

"The prime minister can either have collective cabinet responsibility or his international development secretary, which is it?" he said.

Charles Kennedy - who's not part of the gang on this mission - challenged the prime minister on the legality of America going it alone without a UN mandate.

He pointed to comments from the UN secretary general suggesting that resolution 1441 might not be enough to authorise military action. "Is Kofi Annan wrong?" asked the Lib Dem leader.