LONDON: A year ago this month, America and Britain went to war on Iraq, claiming that Saddam Hussein had secret stockpiles of weapons of mass destruction which were a threat to his neighbours and the world. In fact, Saddam had no such stockpiles and almost certainly no such weapons. So Britain and America went to war on a false prospectus.

I did not support that war, but nor did I actively oppose it. I wrote a column defending a position of "tortured liberal ambivalence". The main reason I sat on the fence was the apparent evidence of concealed weapons of mass destruction which, especially in the wake of the 9/11 attacks, seemed to me a strong argument for intervention. Without it, I would probably have said a clear "no".

So now I want to know: why was I misled? Who duped whom? For, sure as hell, somewhere down the line someone was duped, and someone did the duping. It's not enough to say "well, at least we got rid of a monstrous dictator" and "perhaps it will be the beginning of long-term change for the better in the wider Middle East".

The first statement is true and the second may yet be, but neither is sufficient justification for what we did. I'm as delighted as anyone for those Iraqis who feel liberated but, for reasons I may explain at greater length in another column, the Iraq war cannot be justified retrospectively as a humanitarian intervention.

This discussion of the past is also about the future. As David Kay, the American weapons-hunter who found no weapons, told the Guardian: "The next time you have to go and shout there's fire in the theatre people are going to doubt it". But next time, the fire may be real.

So, why did I believe the weapons claims? Trying to strip the answer to its essentials, I would say "because of what I heard from No 10 Downing Street and what I read in the New York Times".

You may think Blair is a Bliar; I don't. I'm sure he was convinced that Saddam had those weapons and therefore acted in good faith. Why was he convinced? For a start, Saddam had form.

He had constantly violated UN resolutions and obstructed UN weapons inspectors. Then there was the current British intelligence, fed to Blair by the head of the joint intelligence committee, John Scarlett.

If you ask "who dunnit?", as in a game of Cluedo, the answer in the little black envelope could be "John Scarlett, in the cabinet room, with a secret intelligence folder". Blair was clearly far too impressed by the mystique of MI6, but why did the spooks over-egg their own pudding?

Was it that, after suffering the trauma of apparent redundancy at the end of the cold war, Britain's spies had got into the habit of being a little too eager to prove their usefulness to government? Was it that John Scarlett got carried away by the heady proximity to power? There's a real irony in the fact that it's Scarlett, a senior and impeccably loyal British intelligence officer, who's done more harm than any whistleblower to the worldwide mystique of Britain's spies.

I remember officials in No 10 Downing Street at that time, people of great integrity who I've known and respected for years, brandishing the name of Scarlett as if it were a gold standard of scrupulous professional caution.

But then you have to ask: why were the insiders at No 10 so keen to believe the Scarlett files? I suspect the answer is: because they felt the Americans were probably going to "do" Iraq anyway.

There was, I think, a kind of psychological group dynamic in which the key players at No 10 constantly reinforced each other's belief in the firmness of the evidence, rather as the editors of Stern magazine in Hamburg kept reassuring each other that the Hitler Diaries must be genuine.

Yet in fairness we should remember that many reputable weapons experts - including the now disillusioned American David Kay and, it's often forgotten, the British specialist David Kelly - were themselves persuaded that Saddam was hiding some very dirty secrets.

This British story was ultimately a sideshow; the main play was in Washington. There I believed the New York Times, which for me has long been a gold standard of factual accuracy and balance in its news reporting.

Yet now it turns out that the New York Times ran a series of front-page stories about weapons of mass destruction in Iraq which were based on the solitary say-so of highly unreliable Iraqi defectors.

Its reporters were steered to these poisoned sources by the exile leader Ahmed Chalabi and his American neo-conservative supporters. The sad tale is told in fascinating detail in a recent New York Review of Books.

Having said that, one person must surely have known all along that Saddam Hussein had no such stockpiles. That person was Saddam Hussein. And he is the one who might help us clear up this last great mystery of the Iraq war. -Dawn/The Guardian News Service.