Once upon a time there was a left-wing feminist called Yvonne Roberts. In the Sixties she joined sit-ins at Warwick University, where she was taught by the socialist firebrand E P Thomson. In the Seventies she worked for the current affairs series Weekend World, covering the Yom Kippur war, two American presidential elections, the Portuguese revolution, the death of Franco. In the Eighties she lived with the campaigning journalist John Pilger. Together they were involved in the unsuccessful launch of a pro-Labour Sunday newspaper.

Afterwards, she wrote about Broadwater Farm, and inner-city blight, and women in prison, often for the left-wing weeklies New Statesman and New Society.

In 1984 she published Man Enough, an inquiry into contemporary masculinity; in 1994 she published Mad About Women, which asked whether there can ever be fair play between the sexes. It was a morally rewarding, though not particularly remunerative, way of life.

Then, last year, when Yvonne was 44, she decided to write a novel. She sent a proposal to her agent and went to Wales for a long weekend. On the Friday night, her agent phoned the cottage. 'I think we're talking six-figure numbers,' said the agent. 'What does that mean?' thought Yvonne.

Yvonne's agent knew what six figures meant, and auctioned Every Woman Deserves an Adventure for pounds 155,000, plus pounds 45,000 in foreign rights. The book - which features an orgasm workshop in London, virtual sex in the office of Venus magazine, an orgy in Guildford, a threesome in a country hotel, a near-miss with a younger man, a one-night stand with a gigolo and a passionate affair with a male supermodel - was published with a gold embossed fig-leaf on the cover, at pounds 9.99; 22,500 were printed for the first edition.

Now it was time for Yvonne to give an interview to promote her book. She wore a brown silk trouser-suit, which set off her beautiful blue eyes and amber jewellery. Her perfume was strong, her lips glossy, her figure lean.

It was hard to believe that Yvonne - having been told in her twenties that anorexia had left her infertile - was 45 and seven months pregnant with her second child.

What is the moral of this tale? That feminism is dead and superwoman rides again? That socialists in their forties always sell out? That nothing lubricates a book auction better than sex?

The truth is not so simple. For Yvonne Roberts is left-wing and feminist still. The mug of tea she hands me is emblazoned with the legend: 'I support Kirby Unemployed Centre'. She still writes 'ranting essays' and a monthly column for New Statesman & Society; she is a member of Amnesty International; sponsors a Third World child. Last year, she spoke at the Oxford Union against a motion proposed by the reigning Miss World and Jerry Hall urging women to flaunt their bodies.

Glossy superwoman? The large, south London house she shares with a 45-year-old television journalist, Stephen Scott, needs decorating. The interview takes place on a battered sofa while Zoe, her 10-year-old daughter by John Pilger, wearing a 'Women Against Pit Closures' T-shirt, has a water fight in the garden with two friends. There are frequent interruptions from a smelly dog called Sally.

Smug middle age? Doctors' reactions to her pregnancy have not always been sympathetic. 'The first time I went to St Thomas's I was given this thing that looked like a football pools coupon and basically it said I had a one in four chance of having a Down's syndrome baby. It was a bolt out of the blue. During that crucial period, the first three or four months when you're having tests, I did feel 'Oh God, is this worth all the stress?' '

Selling out? Every Woman Deserves an Adventure is no bonkbuster, despite the gold fig-leaf and blurb: 'Can a woman become a Casanova?' The story of a 44-year-old woman trapped in an unhappy marriage, and her journey to independence, it is serious and feminist but also funny. 'I can't stand feminist fiction,' says Roberts. 'You screech to a halt on page 32 when the heroine is given a long diatribe about victimhood and empowerment. Life isn't like that.'

Life, she discovered, was full of 'girlfriends with good jobs, who just seemed to put up with so much rubbish at home. It made me think about how women value themselves. Once you begin to think you're worth something, then all sorts of things happen. That's all I was trying to say. If people buy the book and just have a laugh, that's fine. But if they buy it and say, 'Hang on a minute, this is something to do with my life and maybe I could take a risk now and then,' that's better still.'

Every Woman Deserves an Adventure is sexy. There is a lot of: 'One hand gently pushes me back against the wall, his knee levers open my legs. The fingers of his other hand unzip my trousers . . .'

Says Roberts: 'The publishers wanted red nail varnish on the woman's hands on the cover. I said: 'No, absolutely not.' I know people say this in Hollywood, but the sex has to be part of the plot. This is a book about sex and its place in our lives, but only as a means to an end . . .

'It seems to me there is a paradox at the moment. Everybody is obsessed by sex, but it's a displacement activity. You can't have a sex life until you've really worked out who you are and what you want from life, and why you want it. And once you've done that, then sex takes up a proper place.'

The truth is that left-wing feminists can be sexy and funny both. They can also be serious. Yvonne Roberts's next book is on the subject of children's rights.

'Every Woman Deserves an Adventure' is published by Macmillan at pounds 9.99.

(Photograph omitted)