‘Armed police!’ she shouted into the megaphone. ‘Get out of the vehicles now! Hands in the air! Do not make any sudden movements.’ Five seconds elapsed, then ten. Luke was a few metres behind her and, despite his Kevlar vest and helmet, he felt horribly exposed out there on the pavement. There was simply no cover. He saw Newbold raise the megaphone once more.

‘You have just ten seconds to comply!’ she called out. ‘This is your final—’

Gwyneth Newbold, qualified firearms officer with the Metropolitan Police, and mother of one, did not get to finish her sentence. Luke watched in horror as she appeared to spin round 180 degrees, followed almost instantly by the crack of a bullet he recognized as a high-velocity round.

‘Officer down!’ he shouted, and sprinted forward to pull her to safety. Ducking low, expecting at any second to hear the crack of a second bullet, he grabbed the collar on her Kevlar vest and dragged her behind the nearest cover he could find. It was a grey electrical junction box, just a metre high, but it would have to do. Leaning over to examine her, he could see she was still breathing and conscious, but the bullet had torn into her shoulder where it wasn’t protected by the Kevlar armour. Blood was still pouring from the wound and he searched desperately for something to staunch it with.

‘Front … pocket,’ she gasped, managing to nod down at her chest. Luke ripped open the Velcro fastening on her vest and retrieved a field dressing. In less than ten seconds he had it open, unwrapped and pressed to her wound, just as others were rushing up to help. There wasn’t room for all of them to hide safely behind the junction box so Luke sprinted fast and low to a spot behind a parked car.

The air was still full of the rhythmic thwock of rotor blades and he expected at any moment to hear the ear-splitting fusillade of automatic weapons in response to the shot fired at Inspector Newbold. Those inside the vans clearly had no intention of giving themselves up.

Instead he heard a succession of low reports, like those from a shotgun being fired, followed by the tinkling of glass. And then an eerier silence, broken only by the distant hum of night-time traffic on Euston Road.

Lomatin. The knockout gas. That must be the incapacitant being fired through the vans’ windscreens, he guessed. Luke waited a further ten seconds, then peered around the side of the parked car. He saw three officers, dressed in full chem-bio protective gear and respirators, holding shields in front of them as they advanced towards the two vehicles. Quickly extracting his phone, he called Angela and gave her a brief, breathless running commentary on what was happening.

‘Look, I’m not leaving this location until I’ve sent you visuals on all of the Bravos, okay? That’s what I’m here for.’