In the run-up to the 20th anniversaryof the Chernobyl disaster next week, supporters and opponents of nuclear power have been trading wildly different estimates for the number of people who are likely to die as a result of the radioactivity spread across Europe by the explosion. Fatal cancers will eventually kill 93,000 people according to Greenpeace, 9,000 according to the World Health Organisation and just 1,000 according to one optimistic academic study.

The death toll from the world's worst nuclear accident is of far more than academic interest. The figures are propaganda in the increasingly vociferous debate over whether industrialised countries should resume building nuclear power stations in response to dwindling fossil fuel supplies and the threat from global warming. And Chernobyl's impact on public health is an important practical issue in the worst affected regions of Ukraine, Belarus and Russia, where an epidemic of thyroid cancer among young people is overwhelming oncology services.