‘Five minutes away,’ she said. ‘The traffic is thinner now and they’re moving at about thirty miles per hour. Best you hang back and we’ll see what they do.’

The riders were all tuned in to Button’s frequency and they pulled in to the side of the road. Five minutes later she came back to say that the truck had passed Junction 5 and was still on the M25.

Shepherd’s rider nodded at his two companions. From now on they would be travelling alone and without sirens and lights. The single bike sped off down the approach ramp and joined the motorway traffic. They kept on the hard shoulder until Shepherd saw the traffic car ahead of them. The rider had also seen the police car and he accelerated to bring them alongside. There were two officers in the vehicle. The passenger looked across at them and Shepherd motioned for them to pull in on the hard shoulder.

As soon as the car had stopped Shepherd handed his helmet to the rider and climbed off. He flashed the rider a thumbs-up and got into the back of the patrol car. ‘Hi, guys,’ he said. He pointed ahead. ‘Follow that truck.’

The car edged into the traffic again, and then moved smoothly into the middle lane. Shepherd took out the Glock and checked the action. ‘I’m Dan,’ he said.

‘Alistair,’ said the driver. He was grey-haired and in his early fifties, probably close to retirement. ‘Pleasure to have you on board.’ He seemed totally unfazed by what was going on.

‘Brian,’ said the officer in the front passenger seat. ‘What’s going on?’ He twisted around in his seat and his eyes widened when he saw the gun. He was in his early twenties with a rash of old acne scars across both cheeks.

‘Nobody told you?’ said Shepherd, putting the gun back in his holster.

‘We were just told to keep an eye on that truck ahead, the one with the green container, and that somebody would be joining us,’ said Alistair. He looked at Shepherd in the rear-view mirror. ‘Someone from the Home Office, they said, which covers a multitude of sins.’

‘We need to stop the truck and get the two men out with as little fuss as possible,’ said Shepherd.

‘That explains the Glock, then,’ said the driver, with only the slightest trace of irony in his voice.

‘We’re going to make it seem like a regular traffic stop,’ said Shepherd. ‘Softly, softly, and I’ll approach them on my own.’

‘What do you need us to do?’ asked the younger cop.

‘Absolutely nothing,’ said Shepherd.

Crazy Boy put his foot down on the accelerator and the speedometer needle pushed above fifty miles an hour. Two Knives held out the bag of khat and Crazy Boy took a handful of leaves. He was just about to put them in his mouth when a blue light flashed behind the truck and he heard the blip of a siren. Both men looked in their side mirrors.