‘The Increment,’ said Button. ‘We can’t afford to take any chances with whatever they’ve got in that container.’

‘You don’t know how they’re going to trigger it, Charlie,’ said Shepherd. ‘If the Increment goes in they might panic and detonate.’

‘You think it might be a suicide bomb?’ asked Button.

‘If Crazy Boy is on the run he might think he’s got nothing to lose,’ said Shepherd. ‘But suicide bomb or not, I’m not sure that the Increment is the way to go. Too many cooks.’

‘How do you think we should handle it?’

Shepherd grinned. ‘I thought you’d never ask.’

Two Knives swung his feet up on to the dashboard and stared at the slow-moving traffic ahead of them. ‘It’s Sunday, where are all these people going?’ he asked.

‘It’s a sunny day so people want to go out,’ said Crazy Boy.

‘But go where? To sit in traffic with thousands of other people? The British are crazy. Maybe we should leave the motorway. We can drive up to London on the smaller roads.’

‘We’re safer here,’ said Crazy Boy. ‘Less chance of an accident, less chance of anything happening.’ He pointed up ahead. ‘And look, the traffic’s starting to move.’

He reached over and took another handful of khat leaves. As he chewed a CCTV camera stared impassively down at them.

There were three police motorcyclists parked in front of MI6’s headquarters, their engines running. Button handed Shepherd his motorcycle helmet. He had changed into a regular Metropolitan Police uniform and a yellow fluorescent jacket and had a Glock in a nylon underarm holster. ‘Good luck,’ she said.

Shepherd grinned. ‘At least you’re not telling me to be careful,’ he said. He had a radio transceiver fixed to his belt and he fitted the earpiece before he put on the helmet. ‘Just make sure that the cops are close to the truck, but not too close to be seen. And tell the Increment to hang well back.’ He clipped the microphone to the collar of his fluorescent jacket.

‘Will do,’ she said. ‘We’ll keep tabs on the truck here. If they leave the M25 we’ll tell you but otherwise we’ll assume that you’ll intercept them around about Junction Five, providing that they stay on and head north. But if they leave at the M26 you’ll still be able to get them.’

‘Got it,’ said Shepherd.

‘If they leave the M25 earlier and cut north into central London we’ll let you know and you can do what you have to do.’

‘Charlie, it’ll be fine,’ said Shepherd. Button nodded and Shepherd climbed on to the pillion of the second bike. He tapped the driver on the shoulder. ‘Let’s go,’ he said.