As the British, American and Spanish leaders prepare for their emergency summit, Jack Straw has warned that war is now "much more probable".

The foreign secretary's downbeat statement came as Tony Blair met with a succession of senior cabinet ministers in Downing Street.

Deputy prime minister John Prescott, Labour chairman John Reid and other senior ministers visited Number 10 as the prime minister sought their backing before heading to a key summit in the Azores.

Speaking after his meeting with Blair, David Blunkett said that hopes for a peaceful end to the crisis had been "thrown into complete chaos" by French pledges to veto any second resolution.

"I think the prime minister and our foreign secretary have done everything in their power to ensure that we found a peaceful way through," the home secretary said.

Speaking earlier, the foreign secretary said it was still not too late for consensus on a second resolution to be achieved.

But Jack Straw warned: "The prospect of military action is now much more probable and I greatly regret that."

He also told the BBC that Britain had "full legal authority" to go to war.

But on Saturday it emerged that left wing MPs were stepping up their calls for the government to set out the basis of its legal case for military action.

John McDonnell, acting on behalf of the Socialist Campaign Group, wrote to Commons Speaker Michael Martin asking him to ensure that the advice is made available to parliament.

The move keeps up the pressure on Tony Blair as he heads for his meeting with president Bush and Spanish prime minister Jose Maria Aznar.

The White House insisted that the meeting was a further sign that all efforts were being made to "give diplomacy its last final chance".

But reports suggested that the three allies, supported by Hungary, still do not have the support of even nine states on the security council.

With none of the "middle six" members of the UN security council due to attend the Azores meeting, there was speculation that the leaders would focus on going to war without a new resolution rather than on how to win over other governments.

Meanwhile, further signs that America and Britain were preparing to go ahead with military action came with a pledge to push forward the Israeli-Palestinian peace process.

Blair said it was a sign that the allies were being "even handed" in their approach to the Middle East, but sceptics suggested it was intended to mitigate the consequences of war without UN support.