And so to bed

Are American novelists better at sex than British novelists, so to speak? Are they at least less abashed when thinking - and then writing - of their characters in bed together? Jane Smiley was not disconcerted to be asked about sex in fiction (her novel has many close descriptions of sex, from both female and male points of view), but she was surprised to hear that unhampered sex might distinguish American from British fiction. Had she not heard of the annual "Bad Sex award", given to the worst description of sex in a novel? Though not limited to British authors (Norman Mailer took the prize in 2007) it was a peculiarly British institution, and surely a warning notice to steer clear of closely observed copulation. Smiley looked amazed to hear about it.

She told one interested reader that she had tried to write the sex without breaking tone from what went before and after it. The idea was to describe it as just like other things that her characters did. John Updike, in the course of a long and admiring review of Ten Days in the Hills in the New Yorker, had said that its sexual descriptions "set a new mark for explicitness in a work of non-pornographic intent". A reader at the book club, who confessed to coming from South Dakota, told us how she was aware, as she read, that: "there's a lot of graphic sex here" and wondered at such a novel coming from a "mid-Westerner". "Where I grew up we didn't talk about that." It was evidently not so much an American novel as a Californian novel. "Some people come up to me and tell me how much they like the sex part," Smiley told us. Often these enthusiastic readers, she added, look unlikely connoisseurs of sexual description.

In Boccaccio's The Decameron, the work on which Smiley's novel is modelled, each of the 10 characters gets a day on which he or she can dictate the subject of the stories they tell each other. In Ten Days in the Hills, eight of the 10 characters get sections narrated from their points of view. The two oldest characters, Cassie and Delphine, do not. One reader wanted to know why this was. Had age made them marginal? Why did they have less of a "voice" in the novel? "Cassie says when you reach the age of 70 you have to justify your existence," recalled the reader. "She says that but I don't agree with her," replied the novelist, pointing out that these two characters do talk a good deal. Cassie is allowed to tell one of the best stories of sexual misadventures purloined from Boccaccio.

It was pointed out that (whatever they might secretly get up to) they were the only two characters who do not have sex in the novel. They were removed from the fray. Because we do not enter into their thoughts they are allowed, Smiley suggested, a "dignity" not allowed to the others. The fictional reticence was partly a kind of politeness to one of her sources. Cassie was based on a friend who had supplied her with some of the movie-talk, especially the gossip about old-time Hollywood stars, that is woven into the narrative. She could only be present, in fiction as in life, as an anecdotalist. Delphine, being a mystery to the other characters, also had to be a mystery to the reader, her thoughts left unexposed.

Smiley is a novelistic collector of stories - never more than in Ten Days in the Hills - and was happy to tell us where she had got some of them. A question about her hilarious campus novel, Moo (from a reader who was hungry for a sequel), sent her off into vivid recollections of her years teaching at Iowa State University - and of the horror on the face of the president of the university when she told him that she was writing a campus novel. Smiley's readers seemed steeped in her earlier fiction, but also well versed in her occasional political polemics and even intrigued by the fates of the horses about which she has written.

Her pampered Californian characters had not carried all her admirers with her. One reader confessed that she partly loved Smiley's novels for the ordinariness of her characters, and had found it much harder to care about the spoilt Hollywood types whose loves and conversations make up her new Decameron. These characters, she thought, were "different beings" from those in earlier Smiley novels.

Did the change of milieu simply reflect the "circles" in which she herself had come to move? Smiley resisted the idea that she had been sucked into some different world. She came to the Hollywood characters through her interest in the movies (though she admitted that Max's house in the novel was based on one she had visited for a party.

A different reader worried about the consequences of telling an audience of informed readers the origins of such tales. Stories in Smiley's books that had seemed to this admirer of her writing like inspired flights of fancy were revealed to be based closely on her own experiences. Sometimes explaining elements of a novel stops them being "magical". "It's the whole problem with book groups really." But, like Boccaccio, Smiley was happy to think that stories were only improved by knowing where they came from.

· John Mullan is professor of English at University College London. Next week he will be looking at Quarantine by Jim Crace.