'Dirty bomb' report forces us to think the unthinkable

Could a dirty bomb be the next weapon used by terrorists in London? This scenario was adapted from the report 'Dirty Bombs and Primitive Nuclear Weapons' by Frank Barnaby, one of Britain's leading experts on nuclear terrorism. It was published last month by the Oxford Research Group and describes what might happen.

At 7pm on the same day, Joan Underwood, a hospital physicist at the Chelsea and Westminster, is walking through the ward where medical staff are treating the seriously burnt victims. She has just been monitoring a neighbouring ward where patients have been given a drink of radioactive liquid for diagnostic purposes and has not turned off her Geiger counter. To her surprise, the counter ticks madly. She soon discovers that most of the injured people are radioactive, some very much so. Rapid analysis on the hospital's gamma-ray spectrometer identifies the radioactive material as caesium-137, commonly used in medicine, industry and agriculture, and rarely stored with proper security.

The anti-terrorist police first assume that the explosion in Kensington High Street was another conventional bomb, like the ones that had exploded on 7 July. But it is now clear that it was, in fact, a radiological dispersal device - a dirty bomb. Forensic scientists soon find that Semtex and incendiary thermite had surrounded the radioactive material.

A health physics team from the National Radiological Protection Board at Didcot in Berkshire discovers that a cigar-shaped area stretching 15 miles downwind and five miles across at its widest point is contaminated with radioactivity. This stretches from Kensington to Dagenham, and covers the entire centre of London from Islington to Brixton, taking in Westminster, the City and Canary Wharf.

Meanwhile, Londoners - particularly in the area where the bomb went off - pick up radioactivity on their clothes and bodies and carry it home, contaminating public transport on their way. Vehicles also pick it up and spread it far and wide.

The authorities decide that most of the affected area will have to be evacuated and decontaminated, at a cost of hundreds of millions of pounds, but the radiation is extremely hard to remove from buildings. In the end the only solution is to demolish them. Much of the centre of the London and its greatest landmarks, including Buckingham Palace, the Houses of Parliament, St Paul's Cathedral, the Swiss Re "gherkin" and Canary Wharf, are reduced to rubble.

The site of the 2012 Olympic Games is unusable and they have to be switched to Paris. Jacques Chirac's political fortunes revive as he claims this as a just reward for having opposed the Iraq War. Tony Blair resigns, and Robin Cook overwhelmingly defeats Gordon Brown for the premiership.