'The best mistresses are the ones we know nothing about'

The famous 19th-century courtesan Cora Pearl, a serial mistress in the grand style, was well-known for her titillating dinner parties. She would have herself served up for dessert, reclining naked on a bed of violets on a (presumably very large) silver dish. It seems unlikely that Victoria Griffin, a 20th-century manifestation of the genre, would go to such lengths, even if she could find a sufficiently sturdy platter. Victoria does not look like stereotypical mistress material, despite her black leather trousers. Her make-up and jewellery are discreet, her nails are not red-lacquered talons, her hair is pulled into a ponytail and though she is pushing 35 she looks schoolgirlish. The effect of the sexy trousers is muted by her crisp blouse, white tights and clogs, and her jacket is from Marks & Spencer.

Nevertheless, a mistress she is, and a serial one too. She has come out of the closet to promote her book, The Mistress: Histories, Myths and Interpretations of the Other Women which, she hopes, will encourage others in a similar situation.

Victoria has been the mistress of one married man after another since she started having relationships. She has never wanted the wedding or the children. "I have this blind spot about why people, particularly women, would want to marry. I keep trying to find out and never get a satisfactory answer."

There is nothing, she says, in her background to point to the life she's chosen. Her father was a businessman, her mother a teacher. They were happily married. She cannot understand where her aversion to family life came from. "I can only conclude that one of my parents had a hidden aversion themselves," she suggests. "I didn't start off thinking this was how I wanted to live, it just kind of happened. And then it happened again. And again. I thought 'This can't just be an accident' and I came to the conclusion you do what you do deliberately even if it's an unconscious decision."

So she simply isn't attracted to single men? "The idea of having someone else there the whole time has always worried me rather. I don't want to appear available the whole time. Though I do desire intimacy. I wouldn't want to be completely cut off." And she cannot help admitting to the added thrill of forbidden fruit. "When you do something the first time it's scary, but once a taboo has been broken it becomes easier. One gets to a stage where sex is only interesting if you shouldn't be doing it. It's like an addiction."

Does she ever feel guilty? "I did the first time it happened, but now I've come to the stage of knowing I don't want to wreck someone's marriage, and actually I provide a sort of stability that another woman might not manage to do. Guilt's just a waste of time really." She doesn't worry about breaking up a family? "If you're going to live a certain way there's no point in beating yourself over the head about it. I suppose that I just don't like the whole concept of marriage so I don't worry about it. But then the concept of family and the way you do things hasn't been around long. I'm being morally relative, I suppose," she concedes merrily.

According to Victoria the idea of the rapacious mistress kept in luxury is no more than a cliche these days. Victoria herself says she expects no financial favours from her lovers. "The word courtesan has acquired its resonance through the idea of kept women leading luxurious lives off the man's spare income. But it's an image that arises out of fear, and possibly some jealousy as well." A modern mistress, she says, could be anyone - and quite possibly is no glamourpuss. "The best mistresses are the ones we don't know anything about. They keep it all secret."

One thing that does seem blindingly obvious about this kind of triangle is that the man is getting to have his cake and eat it at the same time, while both the wife and mistress are sharing a ration of the crumbs. And being a mistress involves a degree of compliancy that most wives would balk at. Mistresses talk about lonely weekends, the feeling of abandonment when the man plays happy family holidays in August. "You have to learn not to look forward to things," explains Victoria. "If you plan a couple of days away together you know it can go wrong. You can't let yourself bank on anything. But then it's nice when things do happen because you can't believe they're going to."

She tries not to ditch her friends too often because her lover happens to be unexpectedly free. "But I don't always succeed. I have a small group of close friends who know about my situation, and phases when I see friends who aren't so close - supposing my lover is on a family holiday. But they have to come second." Landmarks like Christmas lose their significance. "You make your own landmarks. I like Christmas on my own, I was never one for family events."

She says that she likes to keep a part of herself separate for work (but lets slip in the book that she'll abandon a project at a moment's notice for an afternoon's frolicking). As a writer, this is all very well, but pity the poor mistress chained to her desk in a nine-to-five job. "This kind of relationship does work best when one or both partners has a certain degree of flexibility," she notes drily.

Wives, in her book, do not get a sympathetic portrayal. Most are naggy and draggy bunch of humourless whingers. "I could be biased," she admits. "It's not a role I really understand." In a confrontational situation, the wife, she says, tends to attack the other woman rather than her erring husband. Victoria has only once been challenged by a territorial wife. "She wrote to me. She said she'd been happy for a few years after their marriage and I remember thinking that wasn't very good and why hadn't she left him before? I was being young and horrible - I've learned more sympathy since then. Looking back, she was very good about it."

For an example of how not to do it, Victoria would point to Monica Lewinsky. "I don't think she's done a very good job as a mistress but she has done well at making a living out of it now, with her book and everything. I'm not sure I would even call her a mistress - the term implies a relationship, not a quick fumble in the Oval Office." Camilla Parker-Bowles, she says, is a better example. "Camilla comes from a whole line of them, of course. She's done as well as anyone could, she has kept remarkably discreet considering the pressure not to be. Whether she can make the transition from mistress to being a wife is another thing. It completely changes the relationship. I like that Sir James Goldsmith quote: 'When a man marries his mistress he creates a vacancy'."

The Mistress, by Victoria Griffin (Bloomsbury pounds 18.99) is published on 23 September.