Wendy, a 34-year-old full-time mother of two from East Sussex, was a 'typical girl about town, with a few long-term boyfriends peppered with a handful of one-night stands on holiday or after a night clubbing'.

I could have worn them every day but after 13 years of greying M&S pants and flesh-coloured bras Peter would have been rightly suspicious.

I ended up stuffing all my new buys inside the legs of a manky old tracksuit.

'The kids stay with their grandparents and I go to a spa or shopping somewhere like New York. I do shop and have a lot of facials and massages but I also go out alone to bars in the evening and five times I've met a man.

'Usually we just have a snog and a fumble but two have come back to my hotel room.

I washed them by hand, locked in the bathroom, and dried them with a hairdryer as I didn't dare hang them up.' Tall, strong-featured and dressed in a cashmere sweater and wool trousers, Sheila is the kind of woman you see in the aisles of Waitrose, the front row of the school carol service.

But once every fortnight or so she tells Peter, 48, a company director, that she's meeting a (well-briefed) girlfriend for dinner.

Female infidelity, however, has a far lower profile and, in popular culture at least, tends to have terrifying consequences.

The two most famous adulteresses in fiction, Madame Bovary and Anna Karenina, came to sticky ends: one poisoned herself, the other threw herself under a train.

Of course, once they're married it doesn't carry on being like in the magazines but their copy of Cosmo is still popping through the door every month shouting six new ways to heighten orgasm tonight and they think, "It's not going to be with him indoors, he's exhausted, but what a lovely idea …"' Once the seed is planted, outlets are everywhere.

Most affairs start in the workplace, and a recent American study showed that women who travel for work are three times more likely to have had two or more concurrent sexual relationships in the past five years than women in general.

Having witnessed the devastation divorce wreaked on their parents' generation, they have no desire to end their marriages. I like cooking with him and gossiping about the neighbours. Sex with Michael is a purely separate thing; it's about erotic abandonment, being seen as just a woman rather than as Peter's wife, or "the doctor" or a mum. Paula Hall, a sex and relationships counsellor and Relate spokeswoman, says that she expects to see a rising number of female clients who have been unfaithful, as the reasons for straying have changed.