Paul Merton isn't just the guy who sits behind a desk on Have I Got News For You? Soon to play Ireland as part of the Bulmers Comedy Festival, he tells Brian Boydabout going from bank clerk to comic, how he "feels Irish", and why he has been doing an improv show every Sunday since 1986

PAUL Merton is seven. He's having a birthday party. He is entertaining the guests with a joke taken from the Beano magazine: "What's yellow and white and goes at 120 miles an hour? A train driver's egg sandwich."

"I knew then that I would be telling jokes for a very long time," Merton says. "I distinctly remember telling myself at my seventh birthday party that I would have to have better jokes for my eighth birthday party and even better ones still for my ninth birthday party. I was like that at that age because I was brought up an Irish Catholic."

Merton is sitting in the sunshine of the Pleasance Courtyard at the Edinburgh Fringe Festival. The sweat is still dripping down his face from the one-hour show he finished approximately 20 seconds ago, and he seems quite pleased by the connection he's just made between his early stand-up career and his Irish Catholic upbringing.

"My mother's from Waterford and I was educated by Irish Catholics. I think every single person in my school in Fulham, London, had an Irish mother. The thing about a Catholic education is that, at the age of five or six, it asks you to deal with very heavy concepts of heaven and hell. That fires the imagination at an early age. And also, if you don't buy into what the church is telling you, it gives you something to kick against.

"You'd be amazed at the amount of well-known comedians who were brought up Catholic - Julian Clary and Paul O'Grady are two just off the top of my head. I'm so interested in this that I actually made a programme for BBC radio about Catholic comedians a few years ago."

His parents now live in Ireland and Merton says he feels Irish.

"I was brought up in England obviously, but I still have a feeling of what it is to be Irish. I don't really have that feeling of what it is to be English. It seems to me that the Irish find it easier to feel Irish than the English find it to feel English, if you know what I mean. I'm in Ireland a lot. I feel very much at home there. I love the Irish way of looking at things and phrasing the language. I was in a bookshop in Ireland recently and a guy came up to me and said, 'Are you who you think you are?'

"My favourite-ever story comes from the time a BBC crew were filming somewhere deep down the country. This is a true story; it actually happened. The crew were in the middle of nowhere and they were looking for somewhere to have lunch. They came to a crossroads, stopped their car and asked this man were there any restaurants around.

"The man said: 'There's a restaurant about one a half miles that way and there's another restaurant about one a half miles in the other direction.' The crew asked him which one was the better restaurant. He said: 'Whichever one you go to, you'll wish you had gone to the other.' That's just fantastic, isn't it?"

Merton says his comedy style says comes from a teenage obsession with Flann O'Brien.

"There was a boy at school called Michael Green and when I was 15 years old he gave me this book to read. It was called The Third Policeman, and I just loved it. I had never read anything like it before and I tracked down everything I could find by Flann O'Brien. The stories are just so beautifully composed: I love the one about drinking a man under the table, where a man is actually boiled down and all his physical attributes are put into a glass, which is then drunk from under the table.

"I love the short stories, all the Keats and Chapman stuff, and I love stuff like the ventriloquists who go on strike and they go to public spaces and start throwing their voices as a form of protest. There are so many echoes of Flann O'Brien in my work."

None more so than the routine that got him his first professional break. "There was this big police story in the late 1970s called Operation Julie, where the police had raided this big LSD-making factory and, because of all the LSD hanging in the air in the factory, some of the police got high on the drug. I remember one of the police officers being interviewed about the experience and I just thought: this was a real Flann O'Brien moment.

"Now, at the time, I would have been 22 and I was working as a bank clerk, but that was only to please my parents. I really wanted to be a comic. The Comedy Store venue in London was then located in a strip joint in Soho - this was before Soho had become gentrified - and I had heard of this thing called an 'open mic' night where, if you wanted to be a comic, you could go along and they'd give you five minutes to see if you were any good. I spent about three months perfecting this sketch where a policeman who has taken LSD is presenting evidence in court.

"These days, doing a gag about someone on acid is a terrible cliche but, remember, this was 1982. It was all about the juxtaposition between the plodding methodical way a policeman presents evidence in court and the weird effects of LSD. The routine worked like a dream and I was so elated by how the five minutes went that I actually walked all the way home that night from Soho to where I was living in Streatham, south London, and that's about a nine-mile walk."

On the then-burgeoning new comedy scene, when French and Saunders and the cast of The Young Ones were Merton's early colleagues, his policeman-on-acid routine became famous and he decided to pack in his job and go full-time.

"I was so buzzed by the really early success of that sketch," he recalls. "It was a massive confidence boost for a comic just starting off, and it got me through the next 18 months. Then I realised I had to have more than a good five minutes to be a real comedian. That was always the problem in the early days. I would start off really well with that sketch and then I used to flounder."

Still, that five minutes was enough to get Merton a TV deal. Before he had been properly blooded as a comic he had his own eponymous Channel 4 series, and was writing a sitcom for his friend Julian Clary called Julian and Dick.

"I had waited all my life to be a comic, so when all these offers came in, I just said yes to all of them. I had all these TV commitments, and then every night I was rushing straight out to play shows at the Comedy Store. I was working so much I had a total mental breakdown and had to book myself into a psychiatric hospital for six weeks."

Just as he entered the hospital, Channel 4 began screening Whose Line Is It Anyway?, the comedy improv show in which he was the star performer. "Because I was on the television, the other people at the hospital would be staring at me thinking, what's that famous guy from the telly doing in here, and this used to really annoy me. I remember bringing it up in a private conversation with my psychiatrist. He had never seen the programme and he thought I was having delusions about being famous. It was only when I gave him some tapes of the programme that he actually believed me."

Merton still works harder than most other big-name comics. "It's my working class background. My dad was a Tube driver on London Underground," he says. "A lot of the things that I do I have been doing for years, so I feel a sense of loyalty to them. I've been doing comedy improv every Sunday night at the Comedy Store since 1986, I've been doing Just a Minute on the radio since 1988, and I've been doing Have I Got News for You since 1990."

Of the latter show, he admits it irks him a little bit that to the public at large he is just "a guy who sits behind a desk and fills in the words in headlines. The show isn't representative of what I do as a comic." The work that really nourishes him is comedy improv, where he and four long-standing friends create a new show each night based on suggestions from the audience.

"I just realised the other day that I haven't done any solo stand-up in 10 years. I love doing stand-up and I will get back to it. But on the last tour I did I found that during the interval I would find myself back in these grungy dressing rooms and I could hear over the theatre's loudspeakers the sound of all the audience during the interval - all this chatter. And there was me sitting there by myself. I'm making it sound like a real tears-of-a-clown story, but I did really miss my improv friends on that tour."

For all of his on-screen affability and chumminess, Paul Merton, 50, remains highly guarded about his private life. His real name is Paul Martin, but on joining Equity he found the name was already taken. So he borrowed the name Merton from the district of London he grew up in.

He has been married twice, first to the actress Caroline Quentin in 1990. They divorced in 1998 and neither ever publicly discusses the relationship.

He remarried in 2003, this time to his longtime girlfriend, the comedian Sarah Parkinson, but tragically she died of breast cancer the same year. Shortly after her diagnosis, this reporter bumped into her and Merton in London. I asked Sarah about her health and Merton breezily replied: "Oh she won't see another Christmas". It was his way of coping.

Merton brings his improv show (see panel) to Ireland next month as part of the Bulmers International Comedy Festival. He has the fondest of memories of performing in Dublin.

"I know this is going to sound like bullshit, but Dublin really is our favourite audience. It's an absolute joy to play in the place and I'm serious about that. And that goes for all five of us in the show. I remember doing a sort of pantomime improv show in Dublin in 1993 with two of the people who are in this current show. We've never had anything like the reception we had during that week in Dublin. The show had to go for 20 minutes longer each night because of the banter with the audience."

Interview over, Merton walks away swigging from his pint of Guinness. But a few minutes later he's back, tapping me on the shoulder.

"I really am serious about Dublin being our favourite place to perform. Seriously, it's true."

Paul Merton's Impro Chums play Dublin's Olympia Theatre on September 7th. See also: www.bulmerscomedy.ie

My first calling: a defence of improv

Merton knows that comedy improv gets a bad press, and that some people view it as a Victorian parlour game for failed stand-ups. "That's because bad improv, of which there's a lot, is really horrendous. It's like bad jazz: you can hear what it's meant to be but it's just so far away from where it should be. There is that element to improv where people who can't write, can't act, can't do stand-up become comedy improvisers. But seriously, it is my first calling."

In Edinburgh, the Paul Merton's Impro Chums show has done so well that the guest list was cancelled for the remainder of the run. "This is the same show that we have been doing every Sunday night at the Comedy Store since 1986, except, of course, it's never the same show. After we say 'good evening' it's all new, and the beauty of each night is that what happened will never happen again.

"Did you know that for the last 12 years, the front row of the Comedy Store every Sunday night has been the same people? That's how different the shows are."