when he decided he was going to allow a musical version of The Commitments to be made - and that he would write the script for it himself - Roddy Doyle reasoned he should probably read his first novel again.

It's not something he had done often. As a rule, he tries not to read his own novels. "I'd much rather read somebody else's," he says. "I'd only go back and read a book if I needed to do it professionally."

This was one of those occasions. So, on a flight from Dublin to London for a meeting about the musical, he picked up his first book and started to read. "I read most of it on the way over on the plane," he recalls, "and I was just howling with laughter. I had to break the spine of the thing to make sure no-one recognised me and saw the vain f***er laughing at his own jokes."

Ah, but they're such good jokes. Doyle was a 27-year-old teacher when he wrote The Commitments, the story of a group of working-class Dublin kids who form

a soul band. Nearly 30 years on, he's returning to the scene of his first triumph with the musical and a new novel, The Guts, which allows us to catch up with Jimmy Rabbitte, the manager of the band in Doyle's first novel. And it's funny too. Though that's not all it is.

If you want to know how good a writer Roddy Doyle is, I suggest you turn to page 33 of The Guts. On that page, Jimmy, who's now a 47-year-old father, is trying to tell his sons Jimmy and Marvin that he's been diagnosed with bowel cancer. The whole page is a compact lesson in how to write dialogue, reveal character and involve the reader. It's written in Doyle's familiar style - concise, clipped, dialogue-heavy, slightly sweary. And, yes, it's funny:

- "They nuke the bad cells - the chemicals, you know," Jimmy says.

- "Sounds good, said young Jimmy.

- "I'm looking forward to it, said Jimmy - It'll be like goin' mad in a head shop."

But then read the next line. "The boys tried to laugh." Such a simple line. Just five words. But as you read it you can feel it thrum with love and fear. It's a reminder of how good Doyle is on family life - its pleasures and sorrows.

Someone - Irvine Welsh, I think - once called Doyle "the Beatles of modern Irish fiction". There's something in that. Though if you ask him, he'll tell you "I want to be the Stones!" But the Beatles comparison works. Doyle reinvented and reinvigorated the Irish novel in the 1980s, and reminded us that popular doesn't necessarily mean populist. And since then he has gone his own way, followed his own tune.

This afternoon we are sitting deep inside London's Palace Theatre - in the guts, you might say. This is where The Commitments musical will open in October. Upstairs they're getting ready for Derren Brown. Down here we're discussing Ireland's recent history, atheism, and whether Hall & Oates are any good. (He thinks they are, but admits he wouldn't have said so 10 years ago).

Jimmy Rabbitte's musical fascism may be one of the few things Doyle has in common with his first and latest character. ("I try to fight it.") If you want to find Doyle in any of his characters, he says, you should look to Paula Spencer, the alcoholic mother in his hugely controversial TV series Family, who he then made the heart of two novels, The Woman Who Walked Into Doors and Paula Spencer. Not in the alcoholism, I should say, but in her attitudes, feelings, "the geography of her childhood" as Doyle puts it.

In short, Jimmy Rabbitte should not be confused with Roddy Doyle. "I still have my bowel. It's still in good working order. No eviction there. I haven't had cancer." But, he admits, he, like Jimmy - like me, for that matter - are in the middle of things. Kids are growing. Parents are growing older. The pattern of life at this moment is the same for him and his character.

"I won't be going to a funeral tomorrow because I'm here. But parents of friends are dying all the time. I was at a funeral last week and I'll probably be at another one quite soon. Friends have died. Friends have had scares, and all the rest of it. So it's in the air - that notion of mortality and the limits of a life. So the good thing about being a novelist is you can use that stuff."

His own kids are 22, 20 and 15. Not so very far away from the age Doyle was when he wrote The Commitments. No longer reliant. "I would have said it's like a form of grief when you realise you're not needed in the same way any more. You don't load the car and go to the pictures any more. You don't go on holidays together. Things are different."

Things are different indeed. Ireland has changed in the years since The Commitments first appeared. Dramatically. Out of the 1980s recession the Celtic Tiger has risen, roared and then eaten its own tail. It was in 2008, when the financial collapse was beginning to make itself felt in Ireland, that Doyle first came up with the idea of revisiting the characters of his first three novels (after The Commitments, Doyle continued to explore the lives of the Rabbitte family in The Snapper and The Van).

"When the word recession started coming up in the daily news broadcasts I noticed that in a lot of cases it was often accompanied by a 1980s soundtrack. So news about things that were going spectacularly wrong today were being accompanied by Annie Lennox ... which isn't fair on Annie Lennox.

"I found it a bit ... I suppose offensive really. The easy nostalgia of people in their late 30s, early 40s, who obviously weren't acquainted with an empty fridge or a father who's been unemployed all or most of his life."

He wanted to write something set in this 21st-century Ireland and the idea came to add the years to Jimmy and see what had happened to him and his in the years since. The brutal rollercoaster ride the Irish economy has been on isn't the only thing that's changed, of course. Doyle talks of the possibility of legislation allowing abortion in certain circumstances now being introduced. "Thirty years ago there were polls to include the unborn in the constitution.

"Thirty years is a long time, but it's not. I was an adult 30 years ago. I was teaching 30 years ago. I regularly had to insist on the fact that I was an atheist so it wasn't appropriate as a teacher for me to bring a class to mass.

"Maybe slightly more than 30 years ago I couldn't go to the cinema on the Friday before Easter Sunday. You still can't get a drink on Good Friday. Not that it's a burning need of mine. But things were curtailed so much and dictated by the church. And now nobody gives a s***."

When did he decide there was no God? "In my late teens, I think. Still in school. 17? It wasn't a big 'dun ... dun ... dun' moment. It just occurred to me, 'I don't believe in this.'

"I went to a Christian Brothers school. Barking mad violent f***ers. I never had the Jesuits with their more subtle, intelligent approach that seems to act like some sort of benign manacle through the lives of politicians and the judiciary and everybody that counts in my country. The Christian Brothers were just barking mad b******s. They would have been part of it. I cannot accept that these eejits somehow represented God. I just went, 'No, God's not there'. I don't remember shouting or roaring about it."

You'd think, I suggest, someone who had endured such an educational background might not have wanted to teach. "I didn't think teaching was necessarily going to be like that. And there were a few good ones."

Was he a good teacher? "I like to think so, yeah. I was very enthusiastic." He meets former pupils regularly. His local team, Kilbarrack United, made it to a national final recently and he was one of the 2000 or so from the area who went to the Aviva Stadium (they lost on penalties). "Nobody was telling me I was a shite teacher or 'do you remember that day in 1984 when you...' Since I gave up the teaching 20 years ago, once or twice I've met people who were less than happy with their education, but not necessarily with me. I rarely encountered discipline problems. Now and again in the early years I'd walk by somebody who was being slaughtered in class and think, 'That hasn't happened to me yet'. It was reassurance. 'If that guy can be torn apart by that class who are OK for me I must be doing something right'."

When it appeared in 1987, The Commitments was a modest success. An indie hit, to use an appropriately musical description. Three years later that wasn't the case when its sequel The Snapper appeared. "The Saturday after it was published it was number one in Ireland and that seemed to me to come out of nowhere. And the filming of The Commitments was starting. There was a fever around town."

Alan Parker's film of The Commitments appeared in 1991 and broke box office records. "The Van came out the same year and was shortlisted for the Booker. They started filming The Snapper, for which I wrote the script. I wrote Paddy Clarke. It came out in '93 and Family was being filmed. All this time just rolled.

"And I had two kids in there somewhere and I met my wife and I was a teacher until 1993."

The fever peaked with Paddy Clarke Ha Ha Ha winning the Booker Prize. Irish fiction had a new contemporary voice that was both commercially successful and critically acclaimed. Doyle was the new face of new Ireland.

"The Commitments was a brand new thing. Urban, funny, you know. No guilt at all in there. So it was just timely and everybody loved it because it was bucking the standard pitch, I suppose. Then Paddy Clarke was everybody's Granny's Christmas present in 1993. I knew Family was on its way and I knew it wouldn't be anyone's Christmas present for their Granny."

It's possibly difficult now to recall quite what a fuss Family caused when it was broadcast in Ireland. A joint BBC/RTE production, directed by Michael Winterbottom, it was an unrelenting vision of poverty and domestic violence. If The Commitments was Dublin on the upbeat, Family came from the darkest, grubbiest corner of contemporary Ireland. Nearly half of the country tuned in to watch the first episode. And if the headlines were anything to go by the next day, at least half of them hated it.

Journalists, politicians, they all weighed in. "Madness" is how Doyle remembers it. "If Family was made today and broadcast, I think people would like it because it was extremely well made. Michael Winterbottom did a brilliant job. The soundtrack was on the ball and the casting was just spectacularly good. It wouldn't cause the same upset. It was unbelievable."

Is it true he got a death threat? "Yeah, yeah."

How did this affect him, you wonder? Well, maybe not as greatly as you might think, he suggests. "The morning after Family had been broadcast it was second item on the news and it was on Talk Radio all day and I was getting phone calls. And I remember in the late morning deciding I'll walk down to the shops and get the paper and a bottle of milk or whatever. Just to walk the couple of hundred yards down to the shops to get life back to an even keel.

"And I remember that walk vividly. Because there was so much hostility [in the media]. So much shouting and roaring. But nothing happened.

"It was the same the day after I won the Booker Prize. There was just this hysteria. I was lying down in the hotel room and the phone rang. Somebody demanding an interview at six in the morning. And it had been a long night so again I said, 'No, I'm not staying an extra day. I'm going home to the babies.' And we came home and there was no food in the house and I said I'll go to the chipper and I went down and around the corner to the chipper and I was standing in the queue and nobody had a clue who I was. And that was brilliant, The guy behind the counter did. He just grinned and didn't say a thing."

In the years since, Doyle has written another five novels, two books of short stories and a number of children's books. They didn't all have quite the impact of his Barrytown novels. Perhaps that was to be expected. "I'm not trying to measure what I do now against what I've done before and I haven't since ... which is just as well."

For a long time, The Commitments - the book and the film - disappeared for Doyle. "I forgot about the film for a while. It was probably psychologically necessary for me to. But I almost lost ownership of The Commitments in any shape or form. The book, the film. Any knowledge of it disappeared off my list of achievements for a while."

But as the years went by and the work piled up he began to feel more comfortable with his beginnings. "I'd written so much it was no longer defining me. Nor was Paddy Clarke. Nor Family. Nor anything else."

And so he's now able to revisit the characters in The Guts and the story in the musical. It does raise a question, though. Would Jimmy Rabbitte approve of a musical of The Commitments?

"That's a good question. It's the first time it's been asked." Doyle starts laughing. "Would he approve of the musical? Well in theory. No more than I would. Isn't if funny? It's such a fundamentally simple question and yet it had never occurred to me. Musicals. Yeah. Shite. The Sound of Music makes me vomit. That bloody awful Abba thing. The masculine side of me tells me that it's crap. It's utterly crap. Yeah, he'd hate the idea. He'd be appalled.

"But in practice he'd think it was a good night out."