He pushed his pram half-way down the alley, then, checking that no one was taking any interest in him, he removed his tea-cosy hat and put it in the pocket of his greatcoat, which he folded and placed under the blankets in the pram. The hair was still matted, the face still unshaven, the smell still nauseating, but the man dressed in a black tracksuit and black trainers now drew himself up to his full height and took one more look up and down the alley. Not even a stray cat to observe him.

He reached into the cornflakes box and pulled out the stock of a rifle. Next, he flicked the lid off the ‘Edinburgh’s finest’ and extracted a small night-vision telescope. Finally he unscrewed the handle of the pram, tapped it gently on the top, and a slim, perfectly weighted barrel slid out. It took him only moments to piece together a Remington M40 sniper rifle. It wouldn’t have been his first choice, but it was the model Ron Abbott favoured. He finally grabbed the Marlboro packet and slipped it into a tracksuit pocket. Moving swiftly towards the building at the end of the alley, he began to climb the drainpipe on its rear wall with the ease of a cat burglar, bringing back memories of the Iranian Embassy siege when he’d been a young lance corporal serving with the SAS, later mentioned in dispatches.

When he reached the top floor, he looked down once again to check if anyone had spotted him. No one had. He’d chosen his vantage point carefully: he was overlooked only by an old warehouse that closed its doors at six o’clock every evening.

He clambered up onto the roof, then crawled slowly across until he reached the other side, where he studied the gap between the two buildings. Ten feet and nine inches divided him from his chosen vantage point. That wouldn’t be a problem. He’d practised the jump several times with the rifle slung over one shoulder, and his average had been just over fourteen feet.

He retraced his steps, then crouched down for a moment before bursting out of the blocks and sprinting towards the edge of the building, reaching top speed on the last stride. With inches to spare, he leapt into the air like an Olympic long-jumper who knew exactly where the take-off board would be, and landed on the roof of the next building with several feet to spare. He knelt down on one knee and caught his breath, not moving again until his heartbeat had returned to a steady fifty-four.

He then crawled across to the edge of the building, but didn’t look down. He’d never told Colonel Parker, his old commanding officer, that he had a fear of heights. After a few more minutes he stood to take in everything around him, and was well satisfied. But then he’d chosen the spot carefully. He was directly above Ron Abbott’s flat, and Abbott, he’d quickly discovered, was a creature of habit. Something that was considered a deadly sin by the SAS, as it made you an easy target for the enemy. Abbott spent every Thursday evening with members of his family at the dogs in Romford, where they were regularly separated from some of their ill-gotten gains. That was invariably followed by dinner at a local nightclub, not known for its cuisine. He usually arrived back at his flat around one o’clock in the morning with a girl on one arm, sometimes on both.