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?’

‘But the radioactivity can be dealt with?’ asked Button.

‘Of course,’ said Dr Wilson. ‘In fact the first time there was a heavy rain shower most of it would be washed away. If there were no rain, a comprehensive washing of roads and buildings would deal with most of the radioactivity. Citizens would be advised to avoid any food or liquids that might have been exposed to radioactive dust but other than that there’d be no other precautions needed. But it isn’t the true risk that matters, it’s the perception that counts. Most of the indigenous population would have no choice other than to stay, but who would visit the site of a dirty bomb by choice? We’ve run numbers on this and we calculate that a dirty bomb in any average-sized city in the country would result in a £20 billion loss in GDP over five years. Quadruple that if it went off in central London. So for any terror group it’s a pretty good return for an investment of a few thousand pounds.’

One of the technicians went over to Button and whispered in her ear. She stood up. ‘If I can just interrupt you, Dr Wilson, there’s something we need to see. We’ve managed to work on an image of the truck leaving the port.’ She nodded at the technician. ‘On the main screen, please.’

The picture of the Athena disappeared from the monitor and was replaced by a computer-enhanced image taken from the CCTV camera at the exit to Southampton Container Terminal. It showed the cab of a truck and the two figures in the driving seat and passenger seat were clearly visible. Young black men wearing baseball caps.

‘That’s Crazy Boy and his sidekick,’ said Shepherd.

‘Isn’t it just,’ said Button.

Crazy Boy reached into the bag of khat leaves, took out a handful and popped them one at a time into his mouth. He held out the bag to Two Knives, and he helped himself. They were sitting on folding chairs at a wooden table in an industrial unit outside Basingstoke, thirty miles to the west of central London. There were two Smith & Wesson revolvers on the table in front of them. The doors of the container were open and two Pakistani men were inside wearing radiation suits and helmets. They were connecting detonators to the tops of aluminium barrels. Two Knives pointed at the container. ‘If they’re wearing suits, why aren’t we?’

‘It’s only dangerous close up,’ said Crazy Boy.

‘That’s what the Arab said, right?’