The other reason Ross had selected that particular spot was because it gave him a clear view of the pub where the birthday celebrations were now in full swing. Two hundred and forty yards – well within the range of the high-powered precision rifle – as the crow flies.

He eased the butt of the rifle gently into his shoulder, and lined up the crosshairs on the telescopic sight on the forehead of one of the bouncers. He held the rifle in that position for two minutes before he lowered his arm and rested.

Ross suspected it would be a long wait before the real target appeared. After all, it was his thirty-fourth birthday. He took the Marlboro packet out of his pocket, extracted six highly polished bullets and stood them up in a straight line like soldiers on parade. Then he settled down to wait, but didn’t for a moment lose his concentration.

The first reveller emerged from the pub just after midnight. Not someone he recognized. The second, who spilled out onto the pavement a few minutes later, was Terry Roach’s uncle Stan, who had been in and out of jail for the past twenty years, and was now rumoured to have been pensioned off by the family.

Ross raised the rifle once again and centred the crosshairs on Uncle Stan’s lined forehead. He pulled the trigger. A small click followed, allowing Stan to go on his way, blissfully unaware he’d been target practice.

Although he didn’t expect the real target to appear for at least another hour, he loaded six bullets into the magazine. Just in case.

Over the next hour a stream of inebriated guests made their way out of the pub and started walking unsteadily in the direction of their homes. Taxi drivers avoided that street, even in the middle of the day.

Then, without warning, the birthday boy appeared. He staggered out of the pub, accompanied by two of his mates who were in no state to assist him.

Ross calmly took out his phone and dialled 999. When an operator asked, ‘Police, fire or ambulance service?’ he said firmly, ‘Police,’ as Terry Roach lurched forward and grabbed at a window ledge to steady himself.

‘Police. How may I assist you?’

‘There’s a gun battle going on in Plumber’s Road, Whitechapel,’ he said, trying to sound breathless.

‘Can I take your—’ But he’d already switched off the phone. He would dispose of it later.

He nestled the butt of the rifle back into his shoulder, and steadied the barrel with his left hand. He centred the crosshairs of the telescope on the enemy’s forehead, just as he had done in Oman, and now in Whitechapel. He lowered his sights to the birthday boy’s right kneecap, his old sergeant major’s words ringing in his ears: Concentrate, breathe normally and squeeze the trigger smoothly in one movement, don’t snatch. He carried out the order and the bullet whistled through the air towards its target. Seconds later Roach sank to the ground in agony, clasping his right leg.