The policeman suddenly started to run. The woman gripped the handlebars of the young man in the wheelchair and seemed to hunch, as if expecting a blow. And then the crowd were all getting to their feet, pointing at something out of camera.

They began to scatter.

Running for their lives.

A black transit van was being driven at speed. It appeared to be heading straight for the crowd but suddenly it mounted the pavement to avoid the young man in the wheelchair. I automatically looked for anything that would make the transit van unique. Dents, scratches, words that had been sprayed over. But there was nothing. There was brown duct tape plastered over the registration plate. Simple but effective.

The crowd had done a runner. Apart from Abu Din, who was wagging an admonishing finger at the black van.

He was still wagging it when Albert Pierrepoint got out of the van. And then another Albert Pierrepoint. The faces of the two kindly uncles scanned the street. At the top of the screen I could see the young uniformed copper on his belly, radioing for assistance. Another kindly uncle sat at the wheel of the transit van, gunning the engine.

‘Albert Pierrepoint masks,’ I said. ‘Nice touch.’

‘And the duct tape over the registration plates is an even nicer touch,’ Whitestone said. ‘Whoever they are, they know exactly what they’re doing.’

Abu Din’s bodyguards were nowhere to be seen as the preacher was bundled into the back of the black van without ceremony. It began to reverse at speed down the suburban street and then it was gone, the street gradually filling with worshippers watching it leave, the uniformed copper slowly getting to his feet.

Billy hit a few buttons and the big screen became the standard CCTV grid of nine, all of them views of fast-flowing evening traffic.

‘The CCTV followed them on the North Circular heading in an anti-clockwise direction and then we lost them. And then we picked them up again.’

The grid was replaced by a single still image of the transit van burning on what looked like the surface of an abandoned planet. In the background I could see the faded sign of a giant oil company.

‘They switched vehicles,’ I said.

‘Disabled the cameras in this abandoned petrol station and torched their old ride,’ Edie said. ‘So we’ve got one CCTV camera for every person in London but it does us no good at all because we don’t know what we’re looking for.’