And yet history still doesn't know the half of it. It has long since ceased to be a matter for debate that the Iraq adventure began in mendacity and ended in calamity. Sir Richard Dearlove's public penitence this week merely confirmed what he had already said privately, and not only has every single one of the original official reasons for the invasion been falsified, they have all been stood on their heads. Now even what many suspected was the ulterior motive - a war for oil - has gone awry

Speaking at the LSE on Wednesday, Dearlove said the government had put "too much emphasis on intelligence" as a justification for the war in order to win parliamentary support. But even before the notorious specious dossiers were compiled - which is what he meant - he had already said with deadly candour in the July 2002 memo, written in greatest secrecy by Dearlove as head of MI6 for the eyes of Blair and his colleagues, that a decision for war had been taken, and that "the intelligence and facts were being fixed around the policy".

He might have added that, while there were no "weapons of mass destruction" in Iraq, there was a great deal of noxious weaponry, which went missing at the time of the invasion and has since been put to dreadful effect. Nor were there any fundamentalist terrorists in Iraq five years ago - Saddam Hussein was a secular tyrant, and had a very short way with Islamic zealots - but today the country is awash with jihadists. Many of them come from Saudi Arabia, whose monarch we have just greeted in such obsequious fashion so that we can continue corruptly to sell his country arms.

As to the idea, flourished after the event by the dreaded liberal hawks as well as neoconservatives, that an invasion would bring democracy to Iraq, it's tempting to say that comment is superfluous. In fact there is still something to be said - and it was said by Jacques Chirac at a meeting with Tony Blair that has been described by Sir Stephen Wall.

While reiterating his opposition to the war that was about to begin, Chirac made a number of specific points. He reminded Blair that he and his friend Bush knew nothing of the reality of war but that he did: 50 years ago, the young Chirac served as a conscript in the awful French war in Algeria, which Iraq resembles in all too many ways. Then he said that the Anglo-Saxons seemed to think that they would be welcomed with open arms, but they shouldn't count on it. In a very percipient point, Chirac added that a Shia majority shouldn't be confused with what we understand as democracy.

He ended by asking whether Blair realised that, by invading Iraq, he might yet precipitate a civil war there. As the British left, Blair turned to his colleagues and said, doubtless with that boyish grin we happily see less of nowadays, "Poor old Jacques, he just doesn't get it." Well, who got it?

Even supposing that it had been possible to spread democracy at gunpoint, it's curious that anyone thought this would actually serve western interests. Reporting recently from Dubai under the droll headline "US promotes free elections, only to see allies lose", Hassan Fattah of the New York Times observed drily that "the paradox of American policy in the Middle East - promoting democracy on the assumption it will bring countries closer to the west - is that almost everywhere there are free elections, the American-backed side tends to lose". Well, yes.

Then there's Blair's apparently sincere belief that he had an obligation to follow Washington's lead, because "it would be more damaging to long-term world peace and security if the Americans alone defeated Saddam Hussein than if they had international support to do so", and that by offering such unconditional support he would "keep the United States in the international system". Absurd in any case as theory, this too has been drastically confuted by events.

As the hair-raising BBC programme No Plan No Peace has just confirmed beyond doubt, the British government had no influence whatsoever on American policy or conduct. Geoff Hoon, the defence secretary at the time of the invasion, has comically and humiliatingly contradicted himself as to whether he did or didn't oppose the crazy decisions to disband the Iraqi army - thereby setting loose large numbers of resentful armed fighters - and to dismiss all Ba'ath party members - thereby denuding the country of administrators. In any case, what is now quite clear is that his views didn't matter one way or the other. If London meekly agreed with Washington, the Americans went ahead; if London shyly expressed reservations, the Americans took no notice and still went right ahead.

Finally there is what has sometimes been dismissed as a conspiracy theory: that it was really a war for oil. This idea looks a little less cranky now that Alan Greenspan, the former head of the Federal Reserve Board, has acknowledged "what everyone knows: the Iraq war is largely about oil". But here again, there was no need to await his verdict. After all, the most powerful man in British politics had told us the same thing even before the war began. "The greatest thing to come out of this for the world economy," said Rupert Murdoch, "would be $20 a barrel for oil."

And so, on top of the whole list of false predictions and collapsed justifications, we have this final absurdity. As both Greenspan and Murdoch have very likely noticed, the price of oil hit a record $96 a barrel yesterday, and is still going up.

In April 2003, our previous prime minister confidently pronounced that "just as we had a strategy for war, so we have a strategy for peace". It is not pre-empting the judgment of history to say with even greater confidence that no good whatever has come out of this war, that no single good reason for it can any longer be adduced - and that "we" had never had any plan at all, not to say the faintest idea what "we" were doing.

wheaty@compuserve.com