It has been a war of lies from the start. All governments lie in wartime but American and British propaganda in Iraq over the past five years has been more untruthful than in any conflict since the First World War.

The outcome has been an official picture of Iraq akin to fantasy and an inability to learn from mistakes because of a refusal to admit that any occurred. Yet the war began with just such a mistake. Five years ago, on the evening of 19 March 2003, President George Bush appeared on American television to say that military action had started against Iraq.

This was a veiled reference to an attempt to kill Saddam Hussein by dropping four 2,000lb bombs and firing 40 cruise missiles at a place called al-Dura farm in south Baghdad, where the Iraqi leader was supposedly hiding in a bunker. There was no bunker. The only casualties were one civilian killed and 14 wounded, including nine women and a child.

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On 7 April, the US Ai r Force dropped four more massive bombs on a house where Saddam was said to have been sighted in Baghdad. "I think we did get Saddam Hussein," said the US Vice President, Dick Cheney. "He was seen being dug out of the rubble and wasn't able to breathe."

Saddam was unharmed, probably because he had never been there, but 18 Iraqi civilians were dead. One US military leader defended the attacks, claiming they showed "US resolve and capabilities".

Mr Cheney was back in Baghdad this week, five years later almost to the day, to announce that there has been "phenomenal" improvements in Iraqi security. Within hours, a woman suicide bomber blew herself up in the Shia holy city of Kerbala, killing at least 40 and wounding 50 people. Often it is difficult to know where the self-deception ends and the deliberate mendacity begins.

The most notorious lie of all was that Iraq possessed weapons of mass destruction. But critics of the war may have focused too much on WMD and not enough on later distortions.

The event which has done most to shape the present Iraqi political landscape was the savage civil war between Sunni and Shia in Baghdad and central Iraq in 2006-07 when 3,000 civilians a month were being butchered and which was won by the Shia.

The White House and Downing Street blithely denied a civil war was happening ñ and forced Iraq politicians who said so to recant ñ to pretend the crisis was less serious than it was.

More often, the lies have been small, designed to make a propaganda point for a day even if they are exposed as untrue a few weeks later. One example of this to shows in detail how propaganda distorts day-to-day reporting in Iraq, but, if the propagandist knows his job, is very difficult to disprove.

On 1 February this year, two suicide bombers, said to be female, blew themselves up in two pet markets in predominantly Shia areas of Baghdad, al Ghazil and al-Jadida, and killed 99 people. Iraqi government officials immediately said the bombers had the chromosonal disorder Down's syndrome, which they could tell this from looking at the severed heads of the bombers. Sadly, horrific bombings in Iraq are so common that they no longer generate much media interest abroad. It was the Down's syndrome angle which made the story front-page news. It showed al-Qa'ida in Iraq was even more inhumanly evil than one had supposed (if that were possible) and it meant, so Iraqi officials said, that al-Qa'ida was running out of volunteers.

The Times splashed on it under the headline, "Down's syndrome bombers kill 91". The story stated firmly that "explosives strapped to two women with Down's syndrome were detonated by remote control in crowded pet markets". Other papers, including The Independent, felt the story had a highly suspicious smell to it. How much could really be told about the mental condition of a woman from a human head shattered by a powerful bomb? Reliable eyewitnesses in suicide bombings are difficult to find because anybody standing close to the bomber is likely to be dead or in hospital.

The US military later supported the Iraqi claim that the bombers had Down's syndrome. On 10 February, they arrested Dr Sahi Aboub, the acting director of the al Rashad mental hospital in east Baghdad, alleging that he had provided mental patients for use by al-Qa'ida. The Iraqi Interior Ministry started rounding up beggars and mentally disturbed people on the grounds that they might be potential bombers.

But on 21 February, an American military spokes-man said there was no evidence the bombers had Down's. Adel Mohsin, a senior official at the Health Ministry in Baghdad, poured scorn on the idea that Dr Aboub could have done business with the Sunni fanatics of al-Qa'ida because he was a Shia and had only been in the job a few weeks.

A second doctor, who did not want to give his name, pointed out that al Rashad hospital is run by the fundamentalist Shia Mehdi Army and asked: "How would it be possible for al-Qa'ida to get in there?"

Few people in Baghdad now care about the exact circumstances of the bird market bombings apart from Dr Aboub, who is still in jail, and the mentally disturbed beggars who were incarcerated. Unfortunately, it is all too clear that al-Qa'ida is not running out of suicide bombers. But it is pieces of propaganda such as this small example, often swallowed whole by the media and a thousand times repeated, which cumulatively mask the terrible reality of Iraq.