Sitting in the attic office of Jane Fallon's enormous Hampstead home, sun streaming through the window, cat padding by, it's hard not to feel envious. Fresh from a successful career as a television producer, Fallon wrote a first novel that was a bestseller last year (she is just back from meetings with Jennifer Aniston, who has picked up the film rights and bagged the lead), and today we're here to discuss her next, Got You Back, tipped to be another bestseller. On top of all that, she seems relaxed, content and incredibly smart. Oh, yes, and she lives with Britain's funniest man, Ricky Gervais.

It would be easy to dismiss Fallon's novels as just more chick lit. Covers featuring stilettos and pencil-skirt-clad bottoms indicate your average “single girl meets man and lives happily ever after” stuff. Read them, though, and you will find something different. “I don't read traditional chick lit any more. That all started 12 years ago; we've grown up now,” says Fallon, 47. “The world's changed, and to still be reading books where the woman is about to turn 30 and is, like, “Oh, my God, I've got to find a man!' doesn't feel real.”

It is a sentiment echoed by her novels. The first, Getting Rid of Matthew, told the story of a mistress who spent the better part of the book trying to ditch the man she had lured away from his wife, and her second sees two women involved with the same man meet, join forces and plot his downfall, leaving them both alone, and much the better for it.

Fallon arrived at this new genre, dubbed chick noir, by trying to deliver something a little more true to life. “I have friends who are 40, single and don't have kids, and they aren't panicking. Everything's changed. Women are having children much later - it feels as if, suddenly, we've been given 10 more years. And I got really irritated with all those women in books who define themselves by whether they could get someone down the aisle.”

That woman is certainly a million miles from Fallon. Sitting barefoot in front of me today, she looks a lot younger than 47. She comes across as laid-back, but clearly does not suffer fools. In her books, the butt of all the jokes are the D-list wannabes for whom her heroine works, and she admits that when it came to the female lead for her film, she “really wanted to avoid anyone who was ditzy or kooky. I find that really annoying. You want someone you know has a brain”. It would be entirely wrong to assume she's not up for a laugh, though. “I can never resist going for the joke, ever,” she says, and confesses that the thing she misses most about office life is “those funny afternoons, where you just run round like a load of children”.

The youngest of a family of five, she was brought up above her father's shop in Harrow and ended up at University College London. In her third year, she came across Gervais in the Student Union bar, and the couple have been together ever since. Unlike the dysfunctional relationships in her novels, theirs is, she says, a very solid one: “It's about being friends and being able to talk to each other. Sharing a sense of humour is hugely important. Also, I'm more shy and quiet, a bit glass-half-empty, and Ricky is definitely glass-half-full, so we balance each other out.” She can't understand couples who spend a lot of time apart. Now she works for herself, she travels with Gervais if he is away for long periods, though he has an office up the road for when he's in London, because, otherwise, “we'd never get anything done”.

Yet for all the happy-ever-after, their relationship is no stereotypical sweetheart story. They have never married, nor had children. Both deliberately so. “It's funny: people look at you quite strangely when you say that. But I really feel that if you're going to have kids, you don't have them because you think 'I'm that age', or, 'It'll patch up my relationship', or, 'I can opt out of work'. And I've just never wanted them.”

Fallon is a living example of the kind of woman she's writing for. Doing things because it's “what you do” is no longer enough for her - or many of us. “If I'd really wanted children, I would have made it work. It's more that emotional thing. I saw it in one of my sisters. Suddenly, she got this broodiness, this real physical, emotional thing, and I remember thinking, ‘If that happens to me, then I'd definitely have one' - and it just hasn't. It would be a bit of a disaster if it happened now.”

Gervais and Fallon are clearly enjoying their success. The house is a bachelor pad for two - all huge sofas, state-of-the-art systems, bright pink kitchen and enormous indoor pool - and a lot of television sets. “We're both telly addicts; we really do stay in with a bottle of wine and watch TV,” she confesses. Sure enough, on the coffee table sits the latest season of Prison Break. When they're not snuggled up with a box set, they visit LA - “It's fascinating to waft around for a few days” - or stroll round the corner to Jonathan Ross's house. But for all the famous mates and Hollywood trips, she is keen to keep out of the public eye. She is dreading our photo shoot, adamant that we make sure she looks like herself. “We tend to be private. People now, they're renewing their marriage vows so they can get a second magazine spread. It's like, here's our child's second christening party.”

Fallon is the polar opposite of a fame-hungry Wag. I ask her how she feels when she is questioned about Gervais, and she tells me that initially she minded, that she used to want to say, “You know, I haven't written a joke book, or about what it's really like to work in The Office, or what it's like to be an Extra. This hasn't happened to me because of who I go out with.”

Got You Back should make this abundantly clear. Fallon has tapped into a moment - or an age - when women no longer feel the pressure to do what everyone around them is doing, but do what's right for them. And hurrah for that.

Got You Back by Jane Fallon is published on Friday (Penguin £6.99). Available at the Sunday Times BooksFirst price of £6.64 (inc p&p) on 0870 165 8585

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