‘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.

The three bikes sped away, heading south. The three riders were experienced and they cut through the traffic like sharks through a shoal of fish. They had a well-practised technique for getting through red lights. The lead bike would hold up the traffic that had the right of way while the bike with Shepherd sped through, then the third bike would move to the front ready to deal with the next set of lights. The riders were so efficient that at no point did Shepherd’s bike drop below thirty miles an hour, and for most of the time they were travelling well above the legal speed limits, sirens wailing and lights flashing.

They were soon driving through Bromley, and the traffic was lighter so they picked up speed.

‘Spider, they’ve just passed Junction Seven,’ said Button. ‘We’re looking at you on the map and I don’t see that Junction Six is going to work so we’ll stick with the original plan and get you on at Junction Five.’

‘Roger that,’ said Shepherd.

‘We have two traffic cars behind the truck, one has eyeball on the vehicle and they’re expecting you,’ said Button.

The three bikes sped south along the A21 and then turned on to the A224. As they approached Junction 5 Shepherd called up Button. ‘Just about to join the M25,’ he said. ‘Where are they?’