Leading article: President Bush is betraying the founding values of his nation

The bitter taste is left of an administration whose response is to deny first and concede later - only when found out

Outlawed weapons and lies about them. Hidden prisons and torture chambers. Human beings in cages. Captives who "disappear". This was Saddam Hussein's Iraq, was it not, and the justification for war? Two and a half years after the invasion, to the eternal shame of the occupiers, it is increasingly the new Iraq as well.

We are observing what must be the worst week for the reputation of the joint United States and British adventure since the revelations of abuse at Baghdad's Abu Ghraib prison. Any hopes in Washington or London that the battle for Iraqi hearts and minds might yet be won have been thoroughly demolished.

First, the US retracted its denial that its troops had used white phosphorus as a weapon during the assault on Fallujah. Then, almost 200 starving and tortured inmates were found in a secret prison in Baghdad. If one such prison exists, it is possible that there are others.

The saga of the white phosphorus admission is another scar on the reputation of US forces - and, by extension, their commander-in-chief. When the charges were made, in an Italian documentary based on eye-witness reports, they were officially denied by the US State Department and, in response to The Independent report, by the US ambassador in London in a letter to this newspaper.

Both denied US forces had used white phosphorus as a weapon. They conceded that white phosphorus had been used at Fallujah, but only as an illumination or obscurant. This is legal. An article in the US military press, however, had provided a detailed assessment of its use as a weapon against insurgents. This was the point the Pentagon was forced to concede.

At the same time, however, the spokesman hedged his comments with technicalities and disclaimers. White phosphorus was not a chemical weapon, it was a conventional incendiary. It was not a banned weapon when used to flush out enemy combatants. It was used only against insurgents, not civilians. The inference was that its use as a weapon in these supposedly limited circumstances was not only legal, but quite acceptable.

It is not. The use of white phosphorus as a weapon in the assault on a city where many civilians remained went beyond the bounds of conventional warfare. It may not, strictly speaking, be a chemical weapon, but it had that effect. Its use was inhumane; it was indiscriminate; it was uncalled for. It raised the spectre of napalm in Vietnam. And whether either the State Department or the US ambassador in his letter were aware that their denials were wrong, the bitter taste is left of an administration whose response is to deny first and concede later - and only when thoroughly caught out.

How often has the US followed this sequence in trying not to answer for its conduct in Iraq? There are the substances: depleted uranium shells, MK-77 firebombs, and now white phosphorus. And there are the methods: the "rendering" of suspects to be interrogated elsewhere; the use of foreign prisons where torture is routine. And always we hear the same weasel words, the same obfuscating technicalities that marked the US response to Abu Ghraib.

There was no real torture, we were told then, only abusive practices which had no higher authorisation. Just a few "bad apples" were responsible. Then the manuals turned up, details of interrogation techniques, accounts of White House hair-splitting over legal definitions, and we were left to wonder where the US administration drew the dividing line between torture and not-torture. It is a degraded administration that considers torture and lethal weapons the raw material for word games.

The white phosphorus admission relates directly to US military conduct; it was ultimately undeniable. So far, no one has admitted maintaining the secret prison in which all the detainees were Sunnis. But this misses the point. This prison was operating in a country where the government, such as it is, can function only thanks to elaborate US protection. Sovereignty may technically have been transferred to Iraqis, but the US bears ultimate responsibility, at the very least for turning a blind eye to abuses that were well known.

And what of the British government in all this? The Ministry of Defence said British forces only ever use white phosphorus as a "smokescreen" - perhaps not the most felicitous choice of word. As for the prison with its starving inmates, the Prime Minister and others professed their surprise and distress, as they had done over Abu Ghraib. Ann Clwyd MP, whose emotional attacks on the inhumanity of the Saddam regime earned her the job of human rights envoy to Iraq, said that it was "shocking", but that she had been aware of Sunni complaints. So why had she not spoken up before, and why had she not lobbied for an investigation before?

Ever since the first orgy of looting in Baghdad after Saddam was toppled, the British government has done its utmost to distance itself in public from the US administration and its unforgivably mismanaged occupation. But it is a dereliction of duty for ministers to wash their hands of responsibility for what is going on. The Prime Minister signed up to the invasion and he is complicit in its aftermath. Iraq was a joint enterprise, albeit one in which Mr Blair was a very junior partner. If our former ambassador in Washington is correct, he had leverage that he failed to use.

The price of that failure is becoming clear. With these unacceptable actions in Iraq, President Bush is betraying the founding values of his nation. He is destroying the good name of America - and dragging down Britain's reputation with it. Mr Blair used to challenge his critics by asking whether Iraq would be better off if Saddam were still in power. In the light of what we now know, it is surely reasonable to ask whether it would be worse.