By Paul Reynolds BBC News Online world affairs correspondent

Blix's still small voice of calm on Iraqi WMD was not loud enough

If there was one man who could have stopped the war in Iraq last year, it probably was not Hans Blix.

He faced a mission almost impossible. He was looking for something which did not exist.

When he duly found nothing, the Americans and British would not accept that absence of evidence meant evidence of absence.

And he was dealing with an Iraqi leader who did not understand that the only thing which could save him was total co-operation.

But, even then, it might not have worked.

UN 'diminished'

Dr Blix's own thoughtful, reasonable character also told against him.

"[I said] it would prove paradoxical and absurd if 250,000 troops were to invade Iraq and find very little Former UN chief weapons inspector Hans Blix

His still small voice of calm was not loud enough.

His book Disarming Iraq, published just in advance of the first anniversary of the war, gives him a chance to say "I told you so" and he does say that.

But he does it in the same quiet, restrained way in which he sought the truth.

He even admits that, at one stage, as late as 20 February 2003 "I tended to think that Iraq still concealed weapons of mass destruction."

But he states his conclusion about the war simply enough: "It was caused by an unjustified armed action by the US and the UK."

He says of Mr Bush and Blair that it was "probable that the governments were conscious that they were exaggerating the risks they saw in order to get the political support they would not otherwise have had."

And he reckons that among the costs were "the damaged credibility of the governments pursuing it and... the diminished authority of the United Nations".

Minds made up?

Despite such conclusions, he is rather generous in his judgment on those who went to war.

"A common denominator of the failures, it appears, was a deficit of critical thinking," he says.

And he does not accuse the Bush administration of orchestrating the move towards an invasion.

"My conclusion was, and remains, that the armed action that was taken was expected but not irrevocably pre-determined."

As often happens with such books by insiders, what really tells are the pen portraits of the players in the game.

And here a picture emerges of some US leaders making their minds up very early on.

A meeting he and Dr Mohamed ElBaradei, the head of the UN's nuclear agency the International Atomic Energy Agency (IAEA) had with US Vice President Dick Cheney in October 2002 is particularly illuminating.

"He stated the position that inspections - if they do not give results - cannot go on forever and said that the US was 'ready to discredit inspections in favour of disarmament'".

"[It was] a pretty straight way, I thought, of saying that if we did not soon find the weapons of mass destruction that the US was convinced Iraq possessed [though they did not know where], the US would be ready to say that the inspections were useless and embark on disarmament by other means."

Blair's conviction

He says that UK Prime Minister Tony Blair, too, was convinced that Saddam Hussein was hiding something.

Blair: Convinced Saddam Hussein was hiding something

In one meeting "Blair said that even the French and German intelligence services were sure there were such weapons, the Egyptians, too.

"[I said] it would prove paradoxical and absurd if 250,000 troops were to invade Iraq and find very little.

"Blair responded that the intelligence was clear that Saddam had reconstituted his weapons of mass destruction programmes."

And that was after Hans Blix had told the UK prime minister that a lot of the intelligence "had not been all that compelling".

At three sites suspected by the British and Americans, nothing had been found.

UK doubts?

Towards the end he reveals a rush by the UK Government to make a last minute breakthrough, by getting Iraq to commit itself to a series of "benchmarks" which would demonstrate its good faith.

Allowing scientists to be interviewed was one of them.

"At 0800 in the morning on 10 March, I had a call from a member of the British mission [to the UN]," Mr Blix writes.

"He apologised for disturbing me at such an undiplomatic hour and asked if I could come to his mission in half an hour to take a call [on a secure line] from his prime minister."

The benchmark plan came to nothing, but it showed that Britain might have harboured some late doubts about military action.

Or perhaps the UK wanted to show Iraqi intransigence.

Ambiguity

If there is a criticism to be made about Dr Blix, it is that he did not end an ambiguity that was often hardened into a certainty.

The ambiguity was that Iraq had not fully accounted for previously admitted quantities of material from which chemical and biological weapons could be made.

This allowed "unaccounted-for material" to be transformed by the hawks into actual and threatening weapons.

Against such certainties, the measured arguments of Dr Hans Blix, evident on every page of this book, did not get far.