Even the most contentious of military ventures requires conduct that is beyond all reproach

There can be only one response to the photographs shown to the Royal Fusiliers' court martial in Germany, and that is repulsion. For citizens of this country, and especially those associated with the armed forces, that repulsion must be mixed with shame. We had hoped, perhaps arrogantly, that the sort of barbarous abuse committed by American troops at Abu Ghraib had been confined to sections of the US military and that "ours" were somehow different. We now know that this was wrong.

Maybe the practices shown in the Abu Ghraib photographs were more shocking and dulled the initial impact of the British pictures just a little. If so, that is still no excuse for what happened. It is invidious to make comparisons and conclude that "their" abuses were "worse" than ours. All abuse is impermissible and a disgrace. Nor can we be confident that the crimes alleged to have been committed by British troops stopped here. The pictures came to light by pure chance, because they were sent to a commercial outlet for developing. While the Pentagon instituted an investigation soon after the first allegations about Abu Ghraib, rampant rumours of abuse by British troops were apparently ignored. It is not at all clear that, without the chance discovery by the two shop assistants, anyone would have been called to account.

One way or another, we have heard much in the past 48 hours that is reminiscent of the initial reaction of the US authorities when the Abu Ghraib exposé first broke. We heard the head of the British army, General Sir Mike Jackson, like senior US officers before him, stress that only "a small number" of British servicemen had been accused of mistreatment and express confidence in the armed forces as a whole - the "bad apples" defence. We heard jaded old soldiers say that such things happen in war; we just used not to hear about it - the modern mass-media defence.

We heard counsel for one of the accused say yesterday, as the Abu Ghraib defendants also said, that he was "just obeying orders" - the Nuremberg defence. And, as with Abu Ghraib again, we heard the arguments in mitigation: the alleged maltreatment at the Bread Basket camp took place amid the general anarchy of the first weeks after the invasion and after perpetual looting of food aid. Living conditions were atrocious; the temperature up to 50 degrees centigrade every day.

None of these arguments, however, alters the fact that the treatment of Iraqi captives as seen in the photographs violates every international safeguard relating to the treatment of civilians during war and contravenes everything that a civilised nation should stand for. In vain did the Prime Minister and other senior politicians express the hope yesterday that these images of brutality "should not be allowed to tarnish the good name of our armed forces". They already have.

And the damage is particularly grave because of the nature of this war and the likely consequences for the British troops still serving in Iraq. When the US and Britain invaded Iraq, they were not defending themselves, but pre-empting a perceived - and it now turns out - non-existent threat. This was a war of choice, justified in part by the "threat", in part by the high-flown ambition to bring freedom and democracy to Iraq. If it was to have any credibility at all, those carrying out this "civilising mission" had to be beyond all reproach. Both the Americans and the British have fallen far short of upholding the values they professed.

The catastrophic state of security in Iraq, less than two weeks before planned elections, compounds the damage. As with the images of Abu Ghraib, these photographs sped around the world courtesy of Arab television stations as soon as they were released. Generally treated with more tolerance than their American counterparts, all British troops now risk being tarred with the same brush: not just as unwelcome occupiers, but as sacrilegious abusers as well. This is a tragedy for the law-abiding majority of British soldiers that could prove costly - both to the mission itself and in lives.