The Creggan man, who infiltrated both the INLA and IRA in the city in the 1970s and 80s, has also warned future agents to ensure they have written contracts with their handlers to ensure they are not "discarded" when their work in completed.

The 47 year-old former RUC Special Branch and MI5 spy said he has been "blackballed" and forgotten about as nothing more than an "embarrassment" to the security forces.

Gilmour has been hunted by former comrades in Derry over the past 25 years and suffers from post-traumatic stress disorder and a heart condition which required surgery a few years ago. Speaking from a secret location in England, the virtually penniless Gilmour said he feels betrayed.

"The people I have dealt with over the last few years, I assume, are from MI5, and they basically don't give a shit about me. A couple of years ago they stopped paying for a counsellor that helped me deal with the flashbacks and the post-traumatic stress I have had to suffer.

"Even my old RUC contacts have stopped returning calls. It's as if I have been blackballed. You risk your life to stop others getting murdered and maimed, but in the end you are forgotten about. You are an embarrassment from the past; you are no longer useful.

"I always thought that, once my career as an agent was over, I would be looked after for the rest of my life. I was an agent of the state, but the state doesn't want to know."

Queen's medal

Gilmour believes he deserves recognition for his "important" work. "I am not asking for a house, all I want is a pension. But when I first started spying on the INLA, and later the IRA, I honestly believed that one day the Queen would give me a medal."

And he warned prospective agents about the "dangerous" pitfalls. "Anyone thinking of infiltrating or working on the inside to bring down terrorist organisations should get it nailed down, on paper, legally binding, that they will receive a pension long after they have retired from this deadly game.

"If I was a young kid, say from the Muslim community in Britain, thinking of working for the State inside one of the Islamic terrorist groups, I would make sure I obtained a contract. Because what happened to me would discourage anyone from signing up as an agent."

From the age of 16, Gilmour served the state as an informer in Derry. In 1983 he gave evidence against dozens of alleged Derry IRA members as a supergrass, although the courts later dismissed his testimony as unreliable.