Our collective failure has been to take our political leaders at their word. This week the BBC reported that the government's own scientists advised ministers that the Johns Hopkins study on Iraq civilian mortality was accurate and reliable. Published in the Lancet ...it estimated that 650,000 Iraqi civilians had died since the American and British led invasion in March 2003. Immediately after publication, the prime minister's official spokesman said that the Lancet's study "was not one we believe to be anywhere near accurate". The foreign secretary ... said that the Lancet figures were "extrapolated" and a "leap". President Bush said: "I don't consider it a credible report". Scientists at the UK's Department for International Development thought differently. They concluded that the study's methods were "tried and tested". Indeed, the Johns Hopkins approach would likely lead to an "underestimation of mortality". The Ministry of Defence's chief scientific adviser ... recommended "caution in publicly criticising the study". When these recommendations went to the prime minister's advisers, they were horrified. Tony Blair was advised to say: "The overriding message is that there are no accurate or reliable figures of deaths in Iraq". At a time when we are celebrating our enlightened abolition of slavery 200 years ago, we are continuing to commit one of the worst international abuses of human rights of the past half-century. Two hundred years from now, the Iraq war will be mourned as the moment when Britain violated its delicate democratic constitution and joined the ranks of nations that use extreme pre-emptive killing as a tactic of foreign policy.