Is the honeymoon over for Bridget Jones and her friends?

Bridget Jones, arm yourself with a glass of chardonnay and a big tissue. In publishing circles, you and your poor relations are no longer wanted.

After one of the most lengthy runs in literary history, the genre of the urban single woman with the chaotic love life (the "knickerbook") is finished. And the search is on for the "big, grown-up love story". So desperate have some publishers become for a good example of this that sums of £500,000 are already being bandied about.

Knickerbooks are still clogging supermarket shelves. But there have been notably mixed reviews for the much-hyped latest example of this genre, Amy Jenkins's Honeymoon, and the industry bible The Bookseller has run a series of pieces lamenting the lack of novels for more mature readers, including one entitled: "When will the Honeymoon be over?"

The Bookseller cites the research organisation Verdict, which says companies will be forced to abandon their fixation with twentysomethings and early thirtysomethings, and concentrate more on older customers who are "affluent, demanding and very poorly catered for".

Jo Frank at AP Watt, among Britain's top women's commercial fiction agents, says many people in publishing had believed for some time the knickerbook bubble had to burst and were surprised it hadn't.

"People are looking for something else. What I've been looking for, and editors I talk to feel the same, is something broader in scope - a big, sweeping love story, old-fashioned, in Thorn Birds territory. Rosamund Pilcher-type novels.

"The Americans want the same. When I was in New York recently an editor said she was sick of knickerbooks, these girls who are dropping their knickers, having lots of casual, cynical sex, wearing Joseph trousers at the Met bar. And they're all set in London - what about the rest of the country?"

One of Ms Frank's recent successes was a six-figure deal for a novel set in Welshpool. "It has a kind of innocence, and warmth instead of slightly cynical one-liners. I had seven publishers bidding for it on the strength of six chapters." Another, by Santa Sebag Montefiore, sister of Tara Palmer Tompkinson, is a sweeping love story set in Argentina.

The leading agent Patrick Walsh of Conville and Walsh says the "Bridget" phenomenon has left little room for more adult readers. "The issue with these emotionally confused twentysomething women is whether in some way 'empathy fatigue' has set in. I'm desperate to find someone for the mother market - the 45-plus readers who have been well served by writers such as Elizabeth Jane Howard at one end and Maeve Binchy at the other. European editors say they want a big, realistic, middle-class love story. They've been saying that for two years now. Something with male/female crossover. The Germans would pay half-a-million for that."

Supermarket sales ensure there is still a big market for knickerbooks, for now. But many publishing figures believe that post-Bridget, as with many imitations, quality has suffered.

An industry source said: "There are a lot of writers who are jumping on the bandwagon because they think it's easy. They read about these headline advances and it's like dot.com envy. Then they write about their own lives."

There is also a view that the general concept has been saturated. There are now at least three new television series focusing on the emotional lives of young urban professionals. Hearts and Bones, Metropolis and the forthcoming Coupling follow in footsteps already well trod by Ally McBeal, This Life, Cold Feet and Wonderful You.

"Women more than men like to read their own lives reflected in the fiction they read," says Ms Frank. "That's why Joanna Trollope is so successful ... it's like their conversations with girlfriends. It's about empathy. But you can have so much of it and women also want to be transported somewhere else."