She thanked Dr Wilson for coming at such short notice and waved for him to take a seat. He sat down, took out a pair of steel-framed spectacles, and began polishing them with a large white handkerchief. He nodded and smiled at everyone in the room, as if making sure that he had their undivided attention. ‘So, I gather that we might have an issue with a dirty bomb somewhere in the country,’ he said. He had a faint West Country accent. ‘The first thing to bear in mind is that in terms of immediate loss of life, a dirty bomb is not especially dangerous. We tend to refer to them as weapons of mass disruption.’ He chuckled at his own joke but stopped when he realised that no one was smiling. He put his glasses on and linked his fingers on the table. ‘What we’re talking about is a radioactive source that is dispersed into the environment, probably by means of a small explosion. The purpose of the explosion isn’t to kill but to spread the radioactivity across as wide an area as possible. It is a completely different animal to an atomic bomb.’ He looked over the top of his glasses at Button. ‘You are certain that we are not talking about a nuclear device?’

‘There are no nuclear devices unaccounted for that we know about, and if there were we’d have picked up intelligence chatter,’ said Button. ‘But we have heard whispers about several groups who are interested in putting together low-tech dirty bombs.’

‘That’s exactly what they are, low-tech,’ said Dr Wilson. ‘Basically all you need is an explosive, which could be as basic as dynamite. And a source of radioactivity, which could be something as simple as hospital waste or components from smoke detectors. If such a device were to be detonated in, say, Trafalgar Square, the initial explosion would cause very little damage and perhaps no loss of life.’ He paused for effect. ‘But the damage it would cause to the economy would run into billions. Literally billions.’

‘And loss of life?’ asked one of the technicians.

‘Short-term there would be no immediate deaths caused by the radioactivity,’ he said. ‘There wouldn’t be enough exposure to cause radiation sickness. I doubt that anyone would show any symptoms of any kind. We’re not talking Chernobyl. What we would see over the decades following the explosion is a slight increase in cancer deaths. More leukaemia among children, more lung cancer and bowel cancer deaths among adults. The increase might only be of the order of a few per cent but considering the millions of people who live in London and who would be exposed to the radioactivity, it would mean hundreds, possibly thousands, of premature deaths.’

He sat back to let his words sink in. ‘But it’s not the deaths that would do the damage to the country. It’s the terror that such an incident would cause. Who would choose to visit London? Or do business there? Can you imagine what would happen to property values?’