'Usually I tell people that I woke up one morning and just decided that I wanted to write," says Peter Farrelly. "But, seeing as we're here for a while, I'll give you the real version."

As you'd expect from a man who created such comic spectacles as Dumb and Dumber and There's Something About Mary, Farrelly at first comes across as a bellowing hurricane of energy and gags. Suddenly, seriousness falls over his face as he explains the origins of his screen-writing career. "When I was at high school I had a girlfriend who I was crazy about. We had our ups and downs but, to cut a long story short, she ended up falling out of a moving car while we were juniors at college. She broke her neck and died instantly. It made a big impact on me. Three years later, when I still wasn't over it, I decided that it would help if I wrote something down about her. That's how it started."

It seems odd that such a tragic event would help produce movies defined by their slapstick and engagingly juvenile humour. But then, there are several things that are unlikely about Peter Farrelly. To an extent, he plays the role of comedy writer/director to perfection: at 42, he is still floppy-haired and goatee-bearded. He wears the baggy cotton clothes of a teenage skateboarder and peppers his conversation with gags as he sits cross-legged and shoeless in his London hotel room. This, presumably, is the Peter Farrelly who has his characters drink urine and electrocute dogs. Then there's the other Peter Farrelly - the one who loses eye contact with you when he speaks about the death of his girlfriend, his horrific brush with a suicide and his teenage encounter with a UFO.

This is the Peter Farrelly who wrote The Comedy Writer, a new novel so touching, honest and cringingly believable that one can hardly believe it came from the same pen that wrote the movies. "Ah well," he comments says. "A movie is just about entertainment. Writing a book is about finding the truth. You want it to be real. When you go to a movie you're likely to sit through it unless it's really horrendous. So you've got the viewer for two hours. But if a reader is about 50 pages into a book and starts to suspect that it's a bunch of baloney, they're not going to go on. And even if they do, what have you achieved if they didn't believe it?"

In his quest for realism, Farrelly had his novel's hero, Henry Halloran, replicate many of his own experiences as a young man in Hollywood. The recently dumped Halloran turns his back on a dead-end sales job in Boston and moves to California with high hopes of selling a screenplay. Within days of arriving, he tries, and fails, to stop a woman jumping off the roof of a building. When he writes an article about the experience for the LA Times, he is contacted by the suicide victim's deeply strange sister, who latches on to him and hinders his bungling attempts to penetrate the film industry.

In a sense, it's a cautionary tale for aspiring screenwriters everywhere, although Farrelly is keen to play down his own Hollywood struggles. "I had less to lose than the character in the book," he points out. After his girlfriend's death, he became determined to find a focus in life. "By the time I was 24, I remember feeling that I would have really disappointed her," he says. "I was working as a salesman but I was horrible at it. I was nothing. So I started to pray every night. My prayer was: 'God, show me a sign of something I can do and that I will love.' After a while I got it into my head that if I wrote about her and my days at high school and college, I would see something that I would like to do."

He soon discovered a passion for the very process of writing and took what seemed like an audacious career decision. "Where I grew up, people didn't become writers," he laughs. "In my mind, it would have been just as easy to become governor. I didn't tell anyone at first because I was embarrassed by it. When I did confess, I would walk into bars and guys I knew would shout, 'Hey, Pete! C'mere! Tell Charlie what you're going to do! Fucking Hemingway here's gonna write a book!' It was a very hard thing to defend because the odds were that it wouldn't work out."

Things worked out far quicker for Farrelly than for his fictional counterpart. During his first nine years in Hollywood, he made money out of writing without actually making a movie. "It's a lot easier to sell scripts than get them made." But there was one crucial similarity between Farrelly's early days in Hollywood and those of his fictional character. "The suicide really did happen. But I had to trim it down for the book because if I told the real story no one would believe it.

What really happened was I was walking down the street near where I worked in LA and I saw a woman on a building. I was the only person around and I managed to get her down by sending the security guard up to her. I talked to her for a while and asked if she'd like to have a cup of coffee with me. She didn't want to hear it and drove away. I took her licence plate number, called the police and told them that this woman was going to kill herself and they had to contact her family or something. They said they couldn't because it would violate her civil rights. Two days later I was walking along the same street when I saw her up on the same roof. Again, I was the only person around. As soon as I saw her, she jumped. It was too weird - I couldn't write that in a book."

That ghastly coincidence is not lost on Farrelly. "I've had a few strange things like that happen to me," he says. "And because of that I'm very aware of... erm... signs."

In The Comedy Writer, Henry Halloran briefly mentions that he saw a UFO when he was young. This is another of the autobiographical details. "I did see a UFO," explains Farrelly. "I've never told this before in an interview. First of all, I'd like to say that that if I hadn't seen a flying saucer, I wouldn't believe it. But I did. And I won't deny it either."

Late one night in 1975, in his home state of Rhode Island, Farrelly was driving along with a friend when a huge rectangular object approached the car. "It was about 300 yards above us," he remembers. "It was huge and there were millions of lights on the bottom. It hovered down the highway and right over our car. The next day I was driving into school when there was this announcement on the radio saying that if anyone had seen a UFO, they should call this number. So I called it and said, 'Yeah, I saw it last night. What was it?' They told me they were just taking a poll. So I told a lot of friends about it and they said I should find out who the people were. So I called back about a week later and the phone number had been disconnected. At the time, and for years afterwards, I thought perhaps it was a secret government weapon. But that was 25 years ago and what I saw that night is still not on public record, so I have to believe it was some sort of UFO."

The sighting has influenced Farrelly's perspective on life ever since. He believes that "we are in prehistoric times now... there are things we have not discovered yet". He also applies this open-mindedness to his career. "I don't exactly believe in fate," he says. "But you've got to realise that it's sometimes not so bad if you don't get what you want."

Nowadays, he pretty much has everything he wants. He is married with one child and another on the way and, with his brother, Bobby, continues to create some of the biggest-grossing comedies of all time. Their latest effort, Me Myself and Irene, stars Jim Carrey and is released later this year. Unlike Henry Halloran, who allows career setbacks to crush his hope, Farrelly puts his own success largely down to a willingness to "stick it out" in Hollywood. Nonetheless, he insists that certain occurrences were somehow inevitable. "Back in 1990, my brother and I tried to be staff writers on Seinfeld," he recalls. "I was very annoyed that they didn't hire us because I knew we would have done a good job. But thank God they didn't! Where would I be now? Writing jokes every day of the week? I write two months per year now, and I find that hard. Things work out for a reason. At least, they have for me."

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