It was growing up in small-town Ireland in the 1970s that gave the investigative reporter Donal MacIntyre his sense of the underdog. Fresh from victory last week in his libel action against the police, he explained that "there's the new Ireland of the Celtic Tiger, and there's the old Ireland of Angela's Ashes. Mine is much more Angela's Ashes."

If the comparison with Frank McCourt's classic evocation of poverty and suffering seems a bit extreme, consider that MacIntyre was one of five children, including a twin brother, brought up by a single mother who worked as a teacher. "It was extraordinarily difficult for her," he says. And the brutality of his schooling in Co Kildare – where beatings were routine, pupils had dusters shoved into their mouths, and MacIntyre witnessed a boy with a stammer having his jaw forced open by a teacher – remains seared into his memory, even at the age of 36.

These experiences, he says, help explain why he turned to investigative journalism, becoming its most celebrated small-screen exponent since Roger Cook started paying unwelcome visits to dodgy dealers. In his BBC series MacIntyre Undercover his exposés of such diverse scandals as football violence and the abuse of models in the fashion industry made for memorable TV, even if there were those who questioned MacIntyre's methods and motivation.

Fighting others' causes is one thing. But fighting your own is quite another. To be criticised for programmes like MacIntyre's is surely all part of the media rough and tumble. So why did he feel he had to go to court just because a film he made about the abuse of people in a care home in Kent was said by the county's police force to be "misleading"?

"This was one of the most sustained attacks on BBC journalism in recent times," MacIntyre says. "There was the slander the police did to everyone involved in care in the community. They said it was a waste of time investigating our findings. They fell into the trap of saying that people with learning disabilities don't have the same rights as the rest of us."

Even with an unreserved apology in the bag, not to mention "substantial" damages, MacIntyre is having trouble getting the episode out of his system. "I don't obsess about anything in the rest of my life, but people do obsess about libel. Usually it's me dealing with other people who've been libelled, and when they go on about it, I think, yeah, right. But I'm afraid I'll bore for England on this one."

MacIntyre has had to get used to defending himself. Even though his Undercover programmes drew audiences of six million, there were accusations that he was more interested in himself than he was in the scandals. It was "info-tainment", with the emphasis on the latter. Certainly when his care home programme came under scrutiny, media Schadenfreude was in the air.

"There was always great discomfort with the idea of the reporter fronting his own show," he says. "But the programme wasn't about me. What was the risk in being discovered in a care home with my secret camera? If it had happened, I'd have just said, 'OK I'm working for the BBC', and then I'd have gone home. The real risk was that the care home would have gone on operating."

MacIntyre likes to stress his background in mainstream investigative journalism on programmes such as ITV's World in Action, and says his approach on Undercover was no different. "If I caught the zeitgeist it's because I think TV is becoming so much less mediated now. People don't buy into this idea of someone telling them what's going on just because they're standing in front of a camera. The difference with me is that I don't want to separate myself from the communities I move into."

The impact MacIntyre has made as a journalist has come at a cost to his personal freedom. For a year after the programme in which he infiltrated the ringleaders of football violence he had to live in a safe house. "The security thing is no longer an issue, but you do have to keep your eyes peeled," he says. "I tend to keep a pretty low profile, just a small group of friends."

He is sufficiently concerned not to want anything revealed about his siblings that might lead to their identification. He has a girlfriend, lives in west London, and relaxes by canoeing on the Thames. When he was younger he was good enough at the sport to compete in the world championships.

Too well-known a face to be able to continue working undercover, he has fronted a series on extreme weather, and has a second series of MacIntyre Investigates next year. With the rapport he strikes up so easily with people and his undoubted rugged charm, isn't MacIntyre potential chat-show host material? "I don't know about that," he says. "I've seen how it's done. There's a lot to it." Might make for a less dangerous existence though.

Biography

1966: Born, Co Kildare, one of five children. Educated locally and at college in Dublin

1990: Journalist on Irish Press

1992: Researcher for sports TV company Transworld

1993: First reports for BBC sports investigative programme On the Line

1995: MA at City University, London

1996: Joins ITV's World In Action

1999: First series of MacIntyre Undercover

2002: First series of MacIntyre Investigates, and Wild Weather