Joanne Mathers, with her husband Lowry and their son Shane. Joanne was shot dead collecting census forms in the city, a murder Willie witnessed

Marked man: Willie Carlin, who now lives in Britain with a new name and identity, believes he could still be shot by dissident republicans

A self-confessed republican informer, who calls himself "Margaret Thatcher's spy" and who infiltrated Sinn Fein to get close to Martin McGuinness, says he still fears he'll be murdered - more than 30 years after he was spirited out of Londonderry on the Prime Minister's private jet when his cover was blown.

One-time country and western singer Willie Carlin, who lives at a secret address in Britain, says he still looks over his shoulder every day and takes extraordinary security measures to protect himself from execution - even though he insists the Provisional IRA would have no reason to kill him.

"I think an attack is more likely to come from the 'young bloods' who are knocking around today. If the IRA wanted to shoot me, they would have done it a long time ago. I believe a lot of those guys have moved on," says Carlin, a former British soldier, who has just published a book about his work with MI5 and military intelligence's Force Research Unit (FRU) for 12 years from the 1970s.

In a wide-ranging interview with the Belfast Telegraph, Carlin insists that he made "a valuable contribution to people's lives" and helped to persuade Sinn Fein to follow the political path, along with McGuinness and Mitchel McLaughlin, whom he calls the "Ant and Dec" of the republican movement.

He adds: "The IRA know I didn't get anyone shot, I didn't go to court as a supergrass and I didn't damage Sinn Fein in any way. Indeed, I spoke at the ard fheis in 1984 about raising funds."

But Carlin says that he realises that dissident republicans could target him "just because I was someone".

"You can never relax. I routinely drive round a roundabout three times and go back the way I came just to see if somebody is following me. And if I am walking along the street, I often look in a shop window to see if there's the reflection of anyone behind me," he admits.

"And you can't claim benefits - apart from child benefit - because the rest of them are all run from Belfast."

Despite his ongoing concerns about his safety, Carlin insists that he wouldn't change a thing about his life and about passing on information about Sinn Fein's strategies to London, where it was regularly perused by Margaret Thatcher herself.

"Maybe I've rose-tinted glasses on, but I believe I did good in the community. I also played a part in getting volunteers off the army road and down the democratic road, when they all entered the city council," he says.

"Sometimes, people forget that Martin McGuinness, who is sometimes branded a traitor, gave up on a lot of his dreams to enter Stormont. We used to talk about blowing the place up. All Ian Paisley had to give up was his pride."

Carlin, who has a new identity, though he had to revert back to his real name when he wanted to get married, adds: "MI5 can give you a new passport and driving licence and National Insurance number, but they can't give you a birth certificate."

Carlin was recruited by MI5 after nine years as a serving British soldier. They wanted him to return to Derry to join Sinn Fein and engage in community work and report back on what they and Martin McGuinness were thinking.

"They told me they didn't want me to inform on the IRA. They warned me to stay away from them, because if I passed on information to my future handlers, the organisation would soon find out what I was doing," says Carlin, who adds that he decided to write the book, Thatcher's Spy, because he wanted to record his part in getting Sinn Fein from where they were in the 1970s to where they are today.

"I wanted to shine a light on the north west, where it all started in 1969. And I wanted to write about what happened to me. I ended up with 145,000 words and the publishers cut it down to 90,000."

Martin McGuinness plays a central role in the book. Carlin claims that McGuinness gave IRA members permission to set up a top INLA man, Patrick Shotter, for arrest after the Droppin' Well bomb in December 1982, which killed 11 soldiers and six civilians.

Carlin, whose cousin was among the injured, says: "McGuinness badly wanted to get rid of the INLA from Derry, because he hated them."

Carlin also says that he saw McGuinness leaving a safe house in Limavady, where he used to meet his MI5 handler.

"He was a passenger in a car and I nearly died. I wondered if he would have heard about me from the MI5 and if I was going to be killed. But nobody said anything to me.

"A week later, the hunger strike was called off. I knew McGuinness was opposed to the hunger strike and, by joining the dots, I thought whatever happened in the house that day might have been part of ongoing meetings between him and representatives of the British government."

Carlin says that he stopped working for MI5 amid concerns over his handler and after seeing McGuinness coming out of their safe house, but he later re-established contact with the security services, this time the FRU, after witnessing the IRA murder of census collector Joanne Mathers near his mother's home in the Gobnascale area of Derry in April 1981.

The 29-year-old mother-of-one had called at the house, saying she was frightened after having just been threatened by republicans, who had urged people to boycott the census in the wake of the hunger strike.

Carlin says he told her it might be better if she left the area and she said, "God bless you" to him, but he later saw a masked man shoot her at another house.

Carlin says that long after he stopped working for the security services he decided to give evidence to the Bloody Sunday inquiry to refute claims that Martin McGuinness had opened fire on Parachute Regiment soldiers before they killed 14 civilians at the civil rights march.

He says he agreed to testify in London after an ex-contact in the Home Office told him of a “ploy” to blame McGuinness for sparking the gun battle in the Bogside.

He adds: “After fears over my security at the actual inquiry, I gave my evidence in my lawyer’s office to a solicitor from the Saville team who was accompanied by a man I later discovered was from MI5, who later redacted my evidence.”

Carlin says he was later approached to give evidence to the Operation Kenova team, led by former Bedfordshire chief constable Jon Boutcher, who was investigating the activities of the double agent called Stakeknife.

Carlin says he owes his life to Stakeknife, because in 1985, he tipped off his handlers that the Derry man’s cover had been blown by his ex-MI5 contact, Michael Bettaney, who was convicted in 1984 of trying to pass British secrets to the Russians.

In jail, Bettaney’s information to IRA prisoners who had befriended him led to Carlin’s unmasking as an informer and the Provos’ internal security unit — the “nutting squad” — were sent to Derry to detain him.

But Stakeknife saved him with a message to his bosses about what was going to happen to Carlin, who was flown out of Derry in Mrs Thatcher’s private jet — a move that still amazes him. But he believes it was prompted by a concern that he was going to give up crucial secrets to the IRA.

Stakeknife is widely believed to be west Belfast man Freddie Scappaticci, but Carlin says he has no idea if that’s true.

“I know that a man called Stakeknife saved my life, but I’d never heard of Freddie Scappaticci. I couldn’t go to court and say he was Stakeknife.”

Carlin says that he has been back secretly to Derry on a number of occasions. But he’s been unable to return to Ireland for family funerals.

He lost a daughter in a road accident five years ago and his son died from sepsis earlier this year.

“I tried to travel across to one of the funerals, but at Stansted airport two men sat down beside me and said, while they couldn’t stop me from going, they wanted me to know they had information that people would be there to see if I turned up. I couldn’t even send flowers, because my details could be traced through the payments to a florist.”

Several weeks ago, Carlin’s sister passed away. He did get to spend a few days with her before she died.

“We had great craic and nobody bothered us at all. But she pleaded with me not to go to her funeral. She thought I would be safe enough, but feared someone would ‘do’ me at her funeral. All that stuff is very sore in my heart.”

But he insists he has no regrets about his life. “I was a British soldier sent in to be an undercover soldier, but when I saw some of the things that were happening, I ended up with divided loyalties.

“I was told that what I was saying about Sinn Fein and Martin McGuinness was nonsense, because the FRU saw him as a murderer.”

Carlin says it might sound strange, but he says if he could turn the clock back, he wouldn’t alter anything about his years as an informer, adding: “I had a ball.

“In many ways, I know now that I was addicted to adrenalin, the biggest high in the world.

“I remember walking over the bridge at one in the morning and knowing in my heart that they had found out about me and that I was going to be shot.

“But I went anyway and then I found out I was worrying about nothing.”

Carlin says he’s heard talk of a film being made from his book. But he dismisses the idea out of hand.

“It would be the most boring film that ever came out,” he laughs, adding that the intelligence services didn’t regard his book as a threat after they demanded to see a draft.

Several insiders had warned Carlin that a number of passages could be edited out, particularly one involving a claim that the former Lord Chief Justice here, Lord Lowry, acquitted 26 suspected IRA men in the Raymond Gilmour supergrass trial after he’d come under political pressure to release them.

Carlin says he was told the Government’s decision was made because many of the defendants were to stand in elections and London didn’t want to stand in the way of Martin McGuinness’s potential political advances.

In the end, only three minor changes were made to the manuscript, which surprised Carlin, who confesses that he and his family are huge fans of Derry Girls, the hit TV series.

“I think it’s a great show. And people miss many of the political messages underneath it.”

Thatcher’s Spy: My Life as an MI5 Agent Inside Sinn Fein by Willie Carlin is published by Merrion Press, priced £15.99

Belfast Telegraph