But now the often murky world of clandestine policing is in the spotlight as Detective Constable Burton (not his real name) has turned on his force. After years of service to the Greater Manchester Police, the officer feels bitter about his bosses and believes he has been cast aside. The difficulties of adjusting to undercover work are also the subject of the current film Donnie Brasco, starring Al Pacino, in which Jonny Depp plays a young Federal Bureau of Investigation agent infiltrating the New York mafia.
In an highly unusual step, DC Burton has spoken out about his treatment and the life of an undercover police officer. In an interview with Police Review magazine he said that he started working undercover in 1990 when he joined the Omega squad, an elite team of detectives in Manchester set up to target football hooligans.
His early work was to infiltrate English football hooligans at the World Cup in Italy and the European Championships in Sweden, where he pretended to be an armed robber.
His next assignment was to act as a drug dealer. "I had my head shaved, I grew a thick beard, and at that stage I weighed about 17 stone. Because I looked the part, I could go anywhere.
"All the time I was undercover, I was isolated from normal policing and the social scene that goes with it. When the villains we wanted came along, I would get to know them, build up a close relationship with them and invite them into my home."
The operations lasted about six to eight months each after which DC Burton would get a new identity. While working undercover his wife and three children only saw him occasionally. "I can remember going to a parents' evening at one school while I was still working undercover as a drug dealer. You could see that both the teachers and other parents didn't want to speak to me, because I looked a bit of an animal," he said.
"People have said to me: `why did you do it? You don't get any more money for it, so why?' But I enjoyed it. I've never regretted doing the job at all ... And I was good at it."
But at the end of 1994 DC Burton says he was informed that he had become "over exposed" and had to give up his double life and return to normal policing. However, he insists that he got little support from the police about finding a new role and became increasingly worried about the safety of his family.
He took 11 months sick leave during which time he separated from his wife and started taking Prozac. He eventually returned to work in January last year but was offered an administrative post.
He said: "People have this image of undercover work being like Spender [the television series set in Newcastle], but it's just not like that.
"My whole life has changed because of the work I did. You can't really tell anyone about what you do, it's not something you can just bring up in conversation.
"I think I've been used as a guinea pig. At the time I left undercover work, there was no re-entry programme. I don't see why I should have to move to another force - we are happy where we live now."
He added: "I've got another 10 years in the job to get my long-service medal. I don't want to be treated like a star, just with the respect I think I deserve."
He is now back with his wife, but his past still haunts him because associates of criminals he has helped to convict remain in circulation. Of one, he says: "I could bump into him at any time, and I'm worried about what he could do to my family if that happens."
David McCrone, assistant chief constable of Greater Manchester Police, said: "The officer concerned is in the middle of a rehabilitation programme and whilst his version of events is wildly innqaccurate it is not my wish to respond in detail in a way which may hamper his recovery.
"A great deal of support has been given to the officer at all levels in the organisation and also by external specialists. We did find him a suitable job in the short term and are currently in the process of retraining him iun the hope that he will be able to take up another job which will make better use of his skills and experience."Reuse content