By Nick Assinder BBC News Online political correspondent

Blix's report was 'not definitive'

Foreign Secretary Jack Straw responded to Hans Blix's latest report on Iraq by slapping down a demand for a March 17 deadline on Saddam to finally surrender or face the worst.

After months of increasingly frantic diplomatic activity, and failure, the opposing sides in the UN have come to yet another crunch time.

And this time there is no way out. Britain, still firmly alongside President Bush, has played its last diplomatic card.

There is nowhere else Tony Blair can now go.

Bluffing?

If other countries, specifically France, Germany and Russia fail to back down, as they appear set to do, he will be forced to go to war without a second UN resolution.

Those countries opposed to war, meanwhile, are now firmly on the spot. If they are bluffing, it has been called.

They have to accept the March 17 compromise or risk the greatest global diplomatic crisis probably since the collapse of the League of Nations.

Dr Blix's latest, and almost certainly final, report to the UN had needed to be pretty definitive if it was to alter the course of future events.

Never before has Tony Blair appeared so isolated or to be taking such risk with his future

But it was not. There was enough in his statement for both sides to use in evidence to support their cases.

The anti-war countries, led by France, pointed to his insistence that Saddam Hussein is now playing ball, albeit reluctantly and partially, with "substantial disarmament".

Worse for Tony Blair, Dr Blix's colleague, Dr ElBaradei also rubbished British intelligence claims over Saddam's attempts to rebuild a nuclear weapons programme.

Britain and America, on the other hand, seized on Dr Blix's remarks that Iraq was not immediately complying with resolution 1441, as demanded.

And Mr Straw, in a passionate speech aimed directly at his French counterpart, insisted the time had now come to replace words with action.

From the instant reaction to his speech - which was in marked contrast to his last performance - it looked like he might be onto something.

French opposition

But his apparent confidence, backed by Downing Street's insistence it expects to win the resolution, may be misplaced.

France was still refusing to compromise in the wake of Mr Straw's words and if those countries opposed to war fail to blink, there is little doubt Mr Blair will follow President Bush into war without them.

That would threaten to open up the greatest rift between UN states in the organisation's history and spark a serious crisis in relations between Britain and its European allies.

Britain and America can now be expected to launch a frantic bout of diplomacy to find a breakthrough

It would also further widen the yawning gap between Mr Blair, his party and even huge swathes of his country.

Never before has he appeared so isolated or to be taking such risk with his future.

The international crisis that has always been lurking in the shadows throughout this affair has now charged into the daylight.

And it is impossible to tell just how much damage will follow in its wake.

Talks ahead

For Tony Blair he will have been forced to make the choice he always knew might one day be before him - UN or the US.

Even before Dr Blix reported, President Bush had made it crystal clear he was going to war against Saddam Hussein.

And only the day before the report, the prime minister had removed the last doubt over what it would take to stop him backing unilateral US action.

The answer was, virtually nothing. However, Britain and America can now be expected to launch a frantic bout of diplomacy to find that breakthrough.

Public persuasion

As has been the case throughout this affair, the prime minister is staking his position on the outcome of the war.

He clearly believes he can win voters around even if he insists on going to war without a second resolution.

A short, relatively clean conflict - with the discovery of chemical and biological weapons stocks in Iraq - will almost certainly see him emerging victorious and with public opinion, at least, behind him.

However, Mr Blair still remains confident that he will get that resolution, and if that happens he will probably get the majority of his backbench rebels finally on his side.