Two Asian men were outside on the landing, one holding the metal case. Jafari ushered them into the flat and locked the door. ‘Welcome, brothers,’ he said.

The man with the case placed it on the table.

Al-Hussain stood up and went over to it. He flicked the double catches and took out the rifle, then carefully screwed the suppressor into the barrel. The two men stood behind him, eyes wide as they stared at the weapon. He attached the telescopic sight, then placed the gun on the table, the barrel lying on the cushion.

He took out the three magazines and loaded each one with five rounds. He placed two magazines at the side of the cushion and slotted the third into the rifle. He waved for Jafari to take away the case, then pulled the black scarf from his pocket and tied it around his head. ‘Brothers, we should pray,’ he said.

The three men joined him. Jafari showed them the direction of Mecca and they began to pray in unison.

‘This is us,’ said Leigh, bringing the SUV to a halt. Bravo One’s bike was parked on the pavement and the man himself was standing by the entrance to the block, still wearing his helmet. Willoughby-Brown’s van was parked on the other side of the road and he was already climbing out.

‘Guys, I need a weapon,’ said Shepherd. He gestured at Willoughby-Brown. ‘My boss there will cover any paperwork that’s needed.’

‘No problem,’ said Graves. He popped the rear door and tapped a six-digit code into the keypad of a metal gun safe. He opened it to reveal two Glocks, a shotgun and three SIG Sauer 516 assault rifles. The SIG516, with its telescoping stock and thirty-round magazine, had replaced the Heckler & Koch G36 as the Met’s assault rifle of choice, but Shepherd figured it would be overkill for what he needed. He took a Glock, ejected the magazine, checked it and slotted it back into place.

Graves relocked the safe as Willoughby-Brown walked over. ‘This isn’t good,’ he said.

‘They got inside before we could do anything,’ said Shepherd.

‘What do you think? The roof?’

Shepherd shook his head. ‘Could just as easily be a flat. This has been well planned.’

‘So what do we do? A house to house?’ He cursed under his breath.

‘We need to start thinking targets,’ said Shepherd. He gestured at the building. ‘You know where we are, right? Half a mile that way is the stadium where they’re holding the world heavyweight fight. It’s full of Russian VIPs, and Islamic State hate the Russians as much as they hate us. And let’s not forget the PM will be there.’

Willoughby-Brown ran a hand through his hair. ‘What do we do? Evacuate? What if they’re just holding the gun here?’

Shepherd glanced at his watch. ‘The main bout is starting soon. There’ll be a riot if you try to shut it down.’ He gestured at the building. ‘There should be CCTV inside. If we can get a look at the footage, we should be able to see where they went.’