A Monstrous War Crime

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, Margaret Beckett, 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 said the research was "robust", close to "best practice", and "balanced". He recommended "caution in publicly criticising the study".

When these recommendations went to the prime minister's advisers, they were horrified. One person briefing Tony Blair wrote: "Are we really sure that the report is likely to be right? That is certainly what the brief implies?" A Foreign and Commonwealth Office official was forced to conclude that the government "should not be rubbishing the Lancet".

The prime minister's adviser finally gave in. He wrote: "The survey methodology used here cannot be rubbished, it is a tried and tested way of measuring mortality in conflict zones".

How would the government respond? Would it welcome the Johns Hopkins study as an important contribution to understanding the military threat to Iraqi civilians? Would it ask for urgent independent verification? Would it invite the Iraqi government to upgrade civilian security?

Of course, our government did none of these things. Tony Blair was advised to say: "The overriding message is that there are no accurate or reliable figures of deaths in Iraq".

His official spokesman went further and rejected the Johns Hopkins report entirely. It was a shameful and cowardly dissembling by a Labour - yes, by a Labour - prime minister.

Indeed, it was even contrary to the US's own Iraq Study Group report, which concluded last year that "there is significant underreporting of the violence in Iraq".

This Labour government, which includes Gordon Brown as much as it does Tony Blair, is party to a war crime of monstrous proportions. Yet our political consensus prevents any judicial or civil society response. Britain is paralysed by its own indifference.

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. It is inexplicable how we allowed this to happen. It is inexplicable why we are not demanding this government's mass resignation.

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. Some anniversary that will be.

• Richard Horton is a doctor and the editor of the Lancet Richard.Horton@lancet.com