He describes it as a game of "high-stakes chess", which required hypervigilance at all times. "My expertise was starting from scratch," he says of his life in the shadows. The final part of Doyle's book tells of the ramifications of the stresses and things he saw as a policeman and his struggles with his mental health are as "edge of the seat" as his adventures in the force His DNA and fingerprints were erased from the national database, and he was assigned a new passport, birth certificate, credit cards, and driving licence. Before joining Greater Manchester Police he had served seven years in the Army, and knew how to handle firearms and explosives, and execute a plan with military precision. It was decided I needed a girlfriend so Nikki (a fellow UC officer) would be dressed to the nines in Jimmy Choo heels with a Gucci or Vuitton handbag.

Certain things came easy to me, and I had an innate drive to succeed. Whatever field I went into, I would put myself up against more educated people, and it gave me fuel”. Based on intelligence he’d gathered, police arrested four gangland figures and found a fully loaded MAC-10-style machine gun and a couple of kilos of skunk in a car. But pretending to be a gangster played havoc with Doyle's home life. In 2009 the convictions of Colin Joyce and Lee Amos marked a turning point in the fight against gun violence in inner south Manchester There he unleashed a hail of bullets on the two unarmed officers, tossed a hand grenade on their dying bodies and then calmly handed himself in at Hyde police station. Pc Fiona Bone (left) and Pc Nicola Hughes (Image: PA) READ MORE TRUE CRIME:• The violent rise and fall of gangster 'White Tony'... devoted Winnie Johnson's other lost boy

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It wasn't long before Shay's prodigious talent caught the attention of the top and he was called upon to join the secret Level 1 undercover unit, Omega. He was given a new identity and his DNA and fingerprints were removed from the national database. All the while, Doyle was working out doggedly and training himself to become an expert on criminal commodities, learning the going rate for everything from a kilo of cocaine to a MAC-10 machine gun.

I’d spent my life at the sharp end, chasing gangsters. Feeling the adrenaline of going through the door, the rush of a big arrest. All that was gone.” I remember watching it all unfold and thinking it was like Northern Ireland in the bad old days," writes Doyle. "There was an air of excruciating tension unlike anything I'd ever witnessed in the police before." To add credibility to his cover story, he worked alongside Nikki, a fellow Level 1 covert operator who dressed up in Gucci and posed as his girlfriend. I want to highlight mental health issues in the police force. Many police officers can’t put their hands up and tell people they’re struggling”. I'm proud of the work I did that kept people safe, that stopped them from being shot dead, that removed guns from the streets. That's what I signed up to do.And a big part of that, he says, is that new officers, without experience in covert work, failed to understand the role. "In the business world, you put experts in their field in charge of certain areas of operation. The police quite often don't follow that model," he says. "Ego hinders management in the police world." Soon he was headhunted by GMP's specialist undercover unit and tasked with infiltrating the city's underworld. All of his old life was removed and he was given a new identity - that of Belfast-raised 'grafter' and armed robber Mikey O'Brien.

This is a fantastic read, I read it from start to finish in 5 hours.....I hadn't intended to but it was that gripping.

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I just don't speak like that. All I had to do was put to use all the attributes I'd been unconsciously collecting all my life." My calm facade belied the rage erupting inside. For 42 days he'd been at large, 42 days that ended in an act of unimaginable horror. I can still see his face. It still haunts me." All the years he had spent learning the ways of the street: how to talk, what to say, how to conduct himself in the company of criminals proved to be gold dust. "Most cops speak in cop language, even when they are off duty - any decent criminal can spot them a mile off," he says. Doyle is not his real name. He was given a new identity when he was medically discharged from the police in 2020 suffering from PTSD. Now in his forties, he feels he has paid a heavy price for his career. "I sacrificed my mental health for it," he says. Raised on the streets of a 'tough Manchester council estate' Shay Doyle could easily have turned to a life of crime. Instead, he ended up playing the part of a gangster and helped bring down some of Manchester's most feared underworld figures.