By Nyta Mann BBC News Online political correspondent

There was no "People's Princess"-style artifice in his performance; instead, blunt in manner and in the words he used, the broadcast tackled that fact head on.

He opened with the acknowledgement that "this course of action has produced deep divisions of opinion in our country".

Unlike the American public - who his brother-in-arms George W Bush spoke to upon Wednesday night's first skirmish - the prime minister's audience has, despite the best efforts of this great persuader, remained stuck in deep scepticism about the need for this war.

With that in mind his message was also a final attempt, even at this late stage with the attacks already under way, to convince us of his case for war.

This is the same case he has taken round the world and which spectacularly failed to gain the international backing he put so much ultimately fruitless effort into winning.

Mr Blair looked tired and drawn as he talked of the need for war

Drawn in appearance, he set out how the old, familiar dangers of the cold war have been replaced.

The new threat is "disorder and chaos born either of brutal states like Iraq armed with weapons of mass destruction or of extreme terrorist groups".

"Both hate our way of life, our freedom, our democracy."

Intelligence he sees as prime minister is alarming enough to fully justify the use of pre-emptive force, he said.

Without that there was the very real possibility of "catastrophe to our country and our world".

Lonely decision

Whether to send troops to war is, as previous prime ministers have attested, one of the loneliest decisions a holder of the post must make.

In the military conflict that has been unleashed Mr Blair is shoulder to shoulder with President Bush.

But he is also to a significant degree on his own before a public and a Labour Party that simply does not believe in this war.

In the end, Mr Blair acknowledged, it came down to him, because it was "my judgement as prime minister" that "this threat is real, growing and of an entirely different nature to any conventional threat to our security that Britain has faced before".

He has imperilled his reputation as a believer in global multilateralism

He has alienated close European partners, who he now wants to help him with the post-war reconstruction of Iraq but who have no wish to deal with him.

He has imperilled his reputation as a believer in global multilateralism, to which US President George Bush's administration has shown disregard.

That was a crucial factor in the impossibility of Mr Blair convincing Britain and his colleagues to go along with him.

Punishing schedule

The prime minister also knows that innocent civilians will die in the conflict.

Foreign Secretary Jack Straw conceded that earlier on Thursday, when he baldly stated "there will be innocent Iraqi people killed".

He also spoke of his government's "terrible calculation" that in the longer-term more Iraqi lives would be saved than will die in the present conflict.

Mr Blair threw himself into a punishing schedule that has lasted for months as he sought to convince others of the need for this conflict.

In taking all these risks, Mr Blair cannot say he was not warned from virtually all quarters to think again

He travelled thousands of miles as he did so, driving himself hard enough for his close aides to be alarmed at the potential effect of his exhaustion on the decisions he was making.

And in taking all these risks, Mr Blair cannot say he was not warned from virtually all quarters to think again.

Now the larger part of what remains for him to do is, like the rest of the world, to watch and await the outcome.