'It could come anytime, anywhere," he says. "I should be dead long ago." It's almost 25 years since he stood in court giving evidence in the North's biggest supergrass trial. "Republicans don't forget. They have memories like elephants," he says. "The IRA ceasefire doesn't apply to people like me. I'll be a target until the day I die."

Beside him sits Marty McGartland who infiltrated the IRA in west Belfast for the RUC Special Branch. Whereas Gilmour is uncomfortable and nervous, McGartland is cocky and defiant: "Don't worry Ray. If the IRA come, I'll knock them to the ground and you can give them a good kicking!"

"You're a ballsy wee f**ker, aren't you?" says Gilmour, laughing. McGartland has escaped the IRA twice. He jumped out a third-floor flat window after being abducted in west Belfast. He was seriously injured in an attempted assassination in England – wrestling with his attacker for the gun saved his life.

"The rule is 'think on your feet'," he says. "The boys coming after you have a script. You make them depart from it and disorientate them. To survive, you need a nose for danger but you must relax in your daily life. Being suspicious of everybody draws attention to yourself."

We're in a hotel in England. Both men have come out of hiding to meet the Sunday Tribune. For security reasons, neither has done a face-to-face interview with a journalist in a decade. "This is MI5's worst nightmare, us sitting here together talking to you," McGartland says with a big grin. He nibbles chocolate biscuits while Gilmour continues watching everybody. The hotel fire alarm goes off. "Run!" shouts McGartland, rolling about laughing.

It's the first time they've met. Although they didn't know each other, Gilmour sent a get-well card to the hospital when McGartland was shot in 1999. After talking on the telephone a few weeks ago, they decided to get together to form Base (British Agents Seek Equality), to campaign against what they say is neglect by the state they so loyally served. "We've been thrown to the wolves," Gilmour says. "MI5 doesn't give a shit about us. We've outlived our usefulness."

'We weren't touts'

To republicans, they're receiving their just desserts. Even in wider Irish society, the informer is seen as a despicable creature turning against his comrades for money and self-gain. "I don't accept that," McGartland says. "We weren't touts who broke under interrogation. We were British agents who joined the IRA at the request of our handlers to save lives. The majority or ordinary people oppose terrorism." The IRA Army Council is unlikely to be hunting them down. But if individual IRA units – particularly in Derry or west Belfast – learned their whereabouts in England, they'd be targeted. If either returned home to live openly, they'd be dead in hours.

Gilmour (47) is battling alcoholism and depression. He also has a serious heart complaint. His third wife Clare, an attractive, well-educated woman, is with him. "I rarely leave the house, and never without Clare. I sit on my own at home crying for hours," he says. "Until I met Marty today, my wife was my only friend. I'm very lonely. I trust nobody. My paranoia about security has driven most of my wife's friends away but, in my situation, I've every reason to be paranoid."

When Gilmour fled Derry, he was given a new name, national insurance number and passport. He has lived in several parts of Britain under the same identity ever since. He says he suffers from post-traumatic stress disorder with flashbacks of his IRA days and nightmares about gunmen killing him. For 10 years, he saw an MI5 psychiatrist. "Six months ago MI5 said they weren't funding the treatment anymore and if I needed counselling, I could pay for it myself.

"How on earth can I do that? I survive on £80 disability benefit a week. Without counselling, I feel like a pressure cooker waiting to explode. I used to have a special MI5 number to ring if I had a problem. Someone would be there 24/7 to help. That's been pulled too. They tell me in security terms I'm now low-risk, which is bollocks. Was Dennis Donaldson low-risk?"

At his trial, Gilmour gave evidence against 31 Derry men and women. "Everybody thinks I got a huge payment afterwards. I received £600 a week for three years – that was it. They got me on the cheap. When I was working for Special Branch, they promised I'd be looked after for life. They said I was a real policeman, with a number in police headquarters, and I believed that. I deserve the same pension as a retired Special Branch officer so I can live the rest of my life above the breadline."

MI5 bought Gilmour a house when he was first resettled. But, he claims, when his second marriage ended, his wife said if he didn't give her the house, she'd expose his identity to the press "so I handed it over". He had one son with her and another son from a 14-year relationship later. Gilmour wanted to move to the US or Australia but was told "they wouldn't have me because I'd been in a paramilitary organisation."

Gilmour and McGartland were both recruited aged 17, but they're very different men. In a trendy brown leather jacket, crisp white shirt, jeans and sneakers, Gilmour looks handsome and distinguished. At first glance, he seems to bear no resemblance to the photographs of the young lad with the moustache who stood in court all those years ago. But look closely and the eyes and nose give him away. He's reserved and softly spoken, with a mid-Atlantic accent.

'Fifty Dead Men Walking'

McGartland (38) is working-class Belfast through and through. His appearance has changed considerably since he fled the North so he doesn't want any description of him published for security reasons. He never shuts up. He's like a market trader, ducking and diving, with an eye for a move. "Here!" he says, tossing a handful of bills at me from the hotel restaurant for which he's paid. "Give these to your newspaper and claim a few quid for yourself!"

He's tee-total. "When I was a police agent, drinking would have been too dangerous in case I said something to blow my cover. I've never needed alcohol to make me happy anyway." McGartland lives at 100 miles an hour. As he talks, he's sending emails on his laptop, thumping the keyboard with one finger – his hands were badly disfigured in the IRA shooting.

A film based on his autobiography, Fifty Dead Men Walking, premiered at the Toronto Film Festival last week. McGartland was unhappy with parts of the script and had been threatening to throw himself (wearing a baseball cap and scarf to hide his face) onto the red carpet on opening night. But discussions with the filmmakers secured him £20,000 and last-minute changes to the movie. He has photos on his laptop of Jim Sturgess, the lead actor. "Isn't he handsome? And him playing me – the ugliest man you've ever met! Jim Sturgess could win an Oscar for this."

When they first met, just before the Sunday Tribune arrived, Gilmour cried as he hugged McGartland. "I had to give him a hankie for god's sake," says McGartland. "I was surprised Ray looked so well. Hearing about his health problems, I expected him to come hobbling in with two walking sticks and a commode and here he is looking like a movie star!" Yet McGartland is concerned about Gilmour: "Ray could kill himself. He's very near the edge and MI5 could push him over."

Gilmour was born in the Creggan, the youngest of 11. He describes his father as "an armchair IRA supporter." He was much closer to his mother whom, he says, was anti-IRA and "knew right from wrong". He was 12 when a cousin was shot dead on Bloody Sunday. It had little impact on him. "I remember standing up in front of our old black-and-white TV when the BBC played 'God Save the Queen' at the end of broadcasting every night, and my father saying to me, 'Sit down or we'll get a brick through the window.'"

He became involved in petty crime. In 1978, he was convicted of robbery. In jail, he was beaten by IRA prisoners. "It pushed me in the direction of working for Special Branch," he says. Under his handler's instigation, he first joined the INLA before moving to the Provos. He earned £200 a week with bonuses for arrests or weapons found. "I remember getting £500 one time. I'd blow the money on drink, horses, and wild, wild women. I never saved a penny. Money was for spending. Every day could have been my last."

Eventually, the IRA became suspicious of Gilmour. He was now married to Lorraine, who knew nothing of his secret life. They had two children. Gilmour suggested a holiday to the Butlins' camp at Mosney. After leaving Derry, he pulled into a lay-by and told Lorraine he was working for the British. "I said she had two choices: to come with me to safety in a military barracks or to go home. She burst into tears. Eventually, she said she'd come with me but I saw the hatred in her eyes."

'I can still see their faces'

More than 100 people were arrested in Derry after Gilmour fled. "Detectives brought me to face them in their cells and accuse them one by one. I knew these guys. I liked many of them, it was just their antics I hated. I can still see their faces – the shock, the anger, the defiance. One said: 'I knew all along you were a tout.'"

Gilmour suffered severe stress. The family were taken to a ski chalet in Cyprus's Trodos mountains. He downed two packets of tranquilisers and a bottle of vodka. His stomach was pumped. They were moved to the Pissouri Beach Hotel but Lorraine made a reverse charge call home giving the name of the hotel. One night Gilmour noticed Arabs at the bar with a pale westerner: it was an IRA-PLO team there to kill him.

He remembers hearing his minders saying: "'He's not one of ours. He's just another criminal who touted to save his hide and earn a few quid.'" Still, he refused Martin McGuinness's promise that he'd be safe if he came home and retracted: "Franko Hegarty [an IRA informer] listened and he was shot dead."

The Gilmours were moved to England but it was too much for Lorraine who decided to go home with the children. "I gave the kids their Easter eggs and then the police drove them to Newcastle airport. I remember them looking out the rear window at me as the car disappeared into the distance." Years later, the police brought him documents to sign from Lorraine asking for their marriage to be annulled and the children's names changed. "I agreed. The kids were told I was dead. I've had no contact with them. Raymond is 27 now and Denise is 26. They are always in my thoughts."

Just before the trial opened, Gilmour's father was abducted by the IRA in an attempt to pressurise him to retract his evidence. Gilmour says: "I was never going to do that. I didn't believe they'd kill him, and there was talk that he might have been a willing hostage." The trial was "one of the worst experiences of my life". It was the last time he heard his mother's voice.

'God forgive you'

She stood up in the public gallery and said: "Raymond, Raymond, don't you know your mother's here? I can't listen anymore to you saying those things about your friends. God forgive you." Gilmour says: "It was heartbreaking but I don't believe she meant those words. She said them out of fear for our family." The judge threw out the case, calling Gilmour a liar. "A political decision," he says.

Gilmour's father died 10 years ago; his mother seven years ago. Police informed him of their deaths. "I heard my father wanted to see me before he died but MI5 said that would be too dangerous. I sent a wreath to the house when my mother died. 'From your loving son', I wrote. It probably went in the bin." Gilmour wants to see his parents' grave, even in a photograph. "I rang the parochial house in the Creggan the other day to ask if they could help. The priest gave me short shrift. 'Ring my secretary,' he said. He was probably afraid."

Gilmour has no contact with anyone in Derry. He is desperate for information about his brothers and sisters. The Sunday Tribune tells Gilmour what his sister Dymphna said to one journalist about him: "I'm so ashamed of Raymond that I go by any other name but Gilmour. His claims he was a police agent are laughable – he was a tout. He should stay in his little hell-hole and leave us alone to live in peace." Gilmour is shocked by what he hears but says: "I was close to Dymphna. I've still affection for my brothers and sisters. I understand why they had to detach themselves from me."

Marty McGartland's family haven't disowned him. "If you think I'm mad, you should meet my mother," he jokes. "She's a wonderful woman. The IRA sent a mass card saying 'the holy sacrifice of the mass will be offered for the repose of the soul of Marty McGartland' but nothing could intimidate my ma." When McGartland was shot, his mother, brother and sister travelled to his hospital bed. He's in regular telephone contact with them.

McGartland was a petty criminal who bought and sold stolen goods – "my nickname was Arthur Daly" – when he was recruited by Special Branch in 1987. He hated the IRA for its 'punishment' attacks on his friends. Initially, he was just asked to watch republicans. Then, he was encouraged to join the IRA. He was living with his girlfriend Angie, who knew nothing of his double life, and their two young sons.

His first codename was "Bonzo" but he didn't like that – "it sounded like a dog" – so he asked to be known as "Agent Carol". "It was after a girl in Craigavon who I'd go down and visit when I fell out with Angie." Some months he earned £3,000 from Special Branch. He saved the money, hiding it behind his mother's bath panel: "I could have up to £20,000 there." By 1992, the IRA was suspicious of McGartland. He was instructed to go to Connolly House, Sinn Féin's Belfast headquarters.

From there, he was taken to a flat in Twinbrook by Paul 'Chico' Hamilton, Gerry Adams's bodyguard, and Jim McCarthy, Adams's driver. He was tied up. After seven hours he asked to go to the toilet. His hands were untied but his ankles remained bound: he hopped to the bathroom. He saw the bath full of cold water: he was to be submerged in it until he confessed. "I thought, 'If I'm to die it'll be on my terms.' I jumped out the window and fell 40ft. I'd taken the glass with me but the cowardly Provo bastards didn't even jump out the window after me. They ran down the stairs."

'I'd have killed him'

McGartland landed on the ground, a bloody mess but alive. His abductors fled. He was resettled in England under the name Martin Ashe. "I've always kept my first name. I would forget to answer to anything else and that would be suspicious. The surname was after Liz Ashe, a girl I once dated from the Shankill."

The RUC gave McGartland a £50,000 house and £40,000 towards furniture and a car. In 1999, the IRA traced him to Whitley Bay, near Newcastle. He was shot seven times but managed to grab the gun when it was pointed at his head, turning it away: "Had I got it off the bastard, I'd have killed him and put the photos of him lying dead on the internet."

McGartland has since moved and has been given a new identity. He has no mobile phone in case his number fell into the wrong hands. Mobile phone company records show the location where a phone is used. These details could end up with the IRA, he says.

McGartland believes he's been treated shabbily by the state. His hand injuries from the shoot­ing mean he can't cook, button clothes, or tie shoelaces. "My [English] girlfriend gave up her job as a hairdresser to look after me. We receive £15,000 in disability benefits a year paid through MI5. But now MI5 have told me to make a fresh claim through the Department of Work and Pensions.

"I can't tell the department's civilian staff the truth about my injuries because it would blow my cover. MI5 has said to say I've been in a car crash. It's a bullshit story with no police or medical reports to back it up. I want the money to which I'm entitled to keep being paid through MI5." McGartland says MI5 don't like him: "They think I'm too big for my boots, too lippy. They expect to hear 'yes sir, no sir, three bags full sir'. They don't like being challenged."

He says he suffers from post-traumatic stress disorder: "My neighbours in Whitley Bay must have thought I was a lunatic because I'd have nightmares and wake up to find myself pulling down the curtains and trying to get out the window." But he's not depressed: "The IRA shouldn't think I'm about to jump under a bus." He encourages Gilmour to adopt a more positive attitude. "Ray, you could talk a glass eye to sleep!" he says.

'At least I was discreet'

Unlike Gilmour, he keeps up-to-date with all Northern news. "I laugh­ed when Gerry Adams's old driver, Roy McShane, was outed as a Special Branch informer. Roy used to shout at my mother, 'Your son's a touting bastard!'" McGartland's laptop screensaver is a photograph of Jim McCarthy, one of his kidnappers, at a friendly meeting with the PSNI after Sinn Féin endorsed policing: "At least I was discreet and met the peelers in private. The Shinners sit down and have tea and biscuits with them in public!" McGartland declares.

McGartland's Belfast girlfriend Angie initially moved to England with him but, like Lorraine Gilmour, she missed home and moved back. He has no contact with his two sons who are now teenagers. "My fear is that they could become IRA supporters," he says. He doesn't want to contact them: "Better to let sleeping dogs lie."

Both McGartland and Gilmour have secretly returned to the North. McGartland's last trip was in November to the Irish leg of the world rally championship at Stormont. "I was right under the Shinners' noses. I laughed when I saw Martin McGuinness's photograph at it in the next day's papers."

Gilmour returned last year with Clare and his two stepsons: "MI5 told me not to but the PSNI said a day trip was okay if I didn't go to Derry. They provided six plain-clothes officers to shadow us. We visited the Antrim coast. I went into the tourist shop at the Giants' Causeway and bought a postcard of an Irishman with a shillelagh. 'Having a nice time. Wish you were here,' I wrote and posted it to MI5."

'I don't blame the system'

Despite their criticisms of the system, Gilmour and McGartland still support it: "I don't blame the system itself, just a few individuals working in it. I don't know where MI5 gets its staff nowadays," Gilmour says. McGartland gave a talk to British intelligence service personnel heading to Iraq to recruit informers there.

Gilmour speaks of "Londonderry". Both men see themselves as British and vote Tory. When Princess Diana died, Gilmour went to mass to pray for her soul. He's laid a wreath at the monument on the Mull of Kintyre for the senior MI5, police and British Army officers who died in the 1994 Chinook crash. Every November, he wears a poppy and even displays one in his car windscreen.

Both men say they don't regret what they did. "I'm very, very proud I was an agent. Ray and I saved lives," says McGartland. They talk of "the buzz and adrenalin rush" they got from their job. But Gilmour wishes he could sleep at night: "I've a legally held gun under my pillow. I still wake every two hours. I think I hear somebody creeping up the stairs.

"The other night I dreamt I went back to Derry and a huge crowd chased after me to kill me – not just IRA men but ordinary people too. Living a lie wrecks your life.

"When I die, I won't even have my real name on my gravestone."