At the same time as he was making his first appearances on television in the Victorian parlour-game bore that goes under the name, Whose Line Is It Anyway?, Paul Merton had a nervous breakdown and was being treated in a psychiatric hospital: "Everything was fine and I was getting better," he says in his flat, perpetually bored-sounding South London accent, "but because I was on the telly, the other patients used to look at me all the time, in the sense of `what's a famous guy doing in here with us'. "So I raised it in a private conversation with my psychiatrist. I told him `People are looking at me all the time because I'm on television' but what I didn't realise is that he had never seen Whose Line . . . so he thought I was having delusions about being famous and people looking at me all the time. So there I am in a psychiatric hospital where even the psychiatrists don't believe a word I'm saying and all I'm thinking is: isn't this just like one of my sketches? Bloody strange." Indeed. But perhaps only as strange as one of the reasons why he ended up in hospital, for which you have to go back to Paul Merton's seventh birthday party. "I was one of those kids who always tried to make people laugh, and I mean always. I started out learning jokes from books but soon thought up my own. I remember distinctly on that birthday being aware that I was going to be telling jokes to people for a long time so I had better be good at it. I remember thinking: "Well, I can make the children at school laugh now, but I've got to do it when I'm eight as well, so I've got to be a little bit funnier then and then when I'm nine . . . and so on. That was my plan, that was how it was going to work. It's mad isn't it?".

Only in that it took him 15 years to act on his "plan". Simmering away as a bank clerk, "to please my parents", he dramatically resigned one day and went to London's Comedy Store to do an open-spot for new, untried performers. "I knew I only had five minutes to make an impression in the Store, so I spent two weeks writing and perfecting a sketch about a policeman who takes acid and then has to give evidence in court. My "plan" was to make every single line in the sketch funny, and I actually practised in front of the bathroom mirror. When I actually did it in the Comedy Store, the crowd really liked it and I was so elated, because of what I had said to myself on my seventh birthday and because I had chucked in my job, that after the gig I walked home the whole eight miles from Leicester Square to Streatham." As word spread around the circuit about this bright new kid on the block, a bevy of television producers picked up on him and beckoned him to TV land. Still operating his "must be better than last year" plan, he found himself by day writing for his own Channel 4 series, Paul Merton - The Series, then dashing around to his good friend Julian Clary's house to co-write the sit-com Julian and Dick before dashing on to the Comedy Store where he was a regular live performer with the Comedy Improv team. "Because I had waited all my life for this to happen, I wasn't going to turn anything down and I worked myself into the nervous breakdown and into the psychiatric hospital," he says, "it was all just so manic and the more I was working, the more excited I was getting. It was a very strange time." Now so laid-back, he's close to horizontal, the 39-year-old is enthused by being able to get away from Have I Got News For You for a few months and get back to doing what he loves: solo stand-up. "I mean, I really like the programme and the money's good but lately they've been cutting out some of what I think is my best stuff and anyway, it's not really representative of what I do as a comic. I've been really buzzing lately, like I haven't been in years, because I'm getting my own show ready for Cat Laughs and I'm going to tour it all over the place later in the year. I know people are probably half-expecting me to be sitting behind a desk making surly comments because that's how I'm perceived but that's not what I do. I'm a storyteller, not someone who fills in the blanks in newspaper headlines." Although nominally an "alternative" comic when he started in the 1980s, Merton didn't have any "anti-Thatcher" gags worth telling and didn't really find education and National Health Service cutbacks suitable material for comedy routines: "Now that people are familiar with Eddie Izzard and that sort of surreal, narrative-driven approach, they'll be better used to the sort of material I do. I was always more interested in talking about spaceships and Brussels sprouts, and things like that, than politics," he says. By way of strained illustration, he repeats one of the jokes he is most proud of: "I told this at a Private Eye party a few years back: During the war, my dad said to me that you don't have to worry about the Blitz. The only bomb that would get you, he reckoned, was the one that had your name on it. That was fine and it calmed me down but it used to worry our neighbours, Mr and Mrs Doodlebug."

Keen to distance himself away from the current vogue of "lads" humour (drinkin' and shaggin' gags) he pulls out some pretty impressive Irish roots to back up his claim that he is massively influenced by Myles na Gopaleen: "My mother is Irish, real Irish, from Waterford. My father is English and they both now live in Cork. I really think the Irish background did help shape my humour, particularly when I read The Third Policeman when I was 18." Highly imaginative and wickedly clever in his solo material, he brings a type of musichall variety feel to his show by dint of his ability to run the gamut of humour from endof-pier to state of the art post-modern ramblings. Aside from the "spaceships and Brussels sprouts" there's also material on animals, xenophobia, buses and biscuits. The width of his subject matter is neatly counterpointed by a constant deadpan expression and near-monotone tone of delivery.

"I think I get that breadth of imagination from being brought up a Catholic," he says, "and a lot of comics I know, like Julian Clary and Sean Hughes, say the same thing. I was educated by Jesuits in England and I do find now, looking back, that Catholicism really did feed my imagination, but probably for the wrong reasons. At the age of seven, the priests are asking you to deal with concepts like heaven and hell and all that kind of heavy stuff. "At an impressionable age, you're being given these concepts that are totally alien to what's around you and either you get a bit scared or you get a bit intrigued. And then when you get a bit older, a Catholic upbringing gives you something to kick against and feeds your imagination in that way also. You'd be surprised by how many stand-ups have been brought up Catholic - it's a good training."

Paul Merton performs at the Watergate, Fri 7.30 p.m., Sat 8 p.m., Sun 8 p.m.