GOOD gracious, it's Marilyn Monroe. That's what I half thought when this glamorous blonde opened the door, peroxide curls, fresh mascara, cute pout, low-cut frock, smooth if ample flesh. The pills must certainly be working. And why not? Grannies of 61 ought to have fun, fun fun.

She'd just come from a local hairdresser, where she goes twice a week. She treats it as her second office, taking her secretary, Jane, and the post, which she opens under the drier, and dictates answers. A bit disconcerting for the other customers? Not at all. There's usually only one other person there. Should she appear annoyed by the dictation and envelope opening, then she might be offered a glass of wine. Fay usually takes a bottle with her. It is a social outing, having her hair done. And also deeply calculating.

'I used to think you should always be yourself, receiving interviewers at the kitchen sink, holes in stockings, hair growing lanker every year, the very image of a woman novelist left over from the Sixties. Then I noticed that American journalists would pick on the holes in the stockings and photographers would always make me look awful. I realised they want you to be made up, to smile and look like a woman should look. So now, my dear, I always do.'

But isn't that giving in to men's preconceptions? 'Why not? We're allowed some little gratifications in life. It is, of course, gross unfairness that pretty women have always got the best jobs, been allowed to sit in the front office while the unattractive were kept in the back. Yes, very unfair. Children spring into life and their first words are 'It's not fair'. I always said to them, why should it be fair? That's what marks us out as human beings, about the only good we do, trying to make our world fair.

'It's still basically true for women that life is unfair, but our view of what is good-looking has changed. Women have more confidence and self-esteem. You don't have to be pretty, though it still helps. I fear that looking good on your book jacket means more people will read you. Better-looking equals you earn more, equals you are more successful, so isn't it better to look your best, hmm?

'Who wants to look natural anyway? All nature does is kill you. When I had my last baby, I said to the doctor I wanted to have it naturally. He looked at me and said it would kill me. Nature is woman's enemy. Nature renders you nubile so you can have babies, then once that process is over, nature throws you away like a withered husk. If it's lack of oestrogen that dries you up, then take it. I started on hormone replacement therapy about 10 years ago and it's been marvellous. It's like a carpet underlay through life. It gives you an expectation, an anticipation, you don't know what will happen next. With old age, we know all too well what will happen next, and you end up unsurprised by the world. How much nicer to be surprised all the time. I gave my mother some HRT when she was 75 - and she instantly started writing a novel. Now, would you like some coffee?'

We'd come down the hall into the dining room, and all I'd said so far was that remark about M Monroe. Fay Weldon's talk is seamless, not often making complete sense, often lacking logic, and she usually ends up contradicting herself, but it's always entertaining, occasionally original. But you have to catch her in the right mood. Sometimes she can appear a right Dilly Dream, muttering to herself, blinking away, lost in space. At parties she tends to stand on her own, waiting for people to move into her, which means she gets lumbered with all the bores. 'Oh, I never think people are bores. I am grateful if anyone talks to me. I am very uncensorious in real life. Only when I start writing do I change. And it's only since I started writing successfully that I have changed completely as a person.'

She was born Franklin Birkinshaw, not something she likes being reminded of. She has been known to lie, saying Fay has always been her name. Or perhaps Frances. 'The other day, when the tabloids were hounding me in Somerset, I said I was Fay Weldon's sister, Frances. I could just see her . . .' For a moment, her Dilly Dream face appeared, contemplating another persona.

On her birth certificate, after the name Franklin, it has the word 'boy' crossed out. That was when her mother began to realise that Franklin after all was a rather silly name. 'She chose it because the numbers of the letters add up exactly to William Shakespeare.' 'Excuse me?' 'Oh, I don't understand it either, but a lot of people believe it. You'll probably find that the number of your name adds up the same as Mussolini's' Thanks a bunch.

She should have been born in New Zealand, where her father, a doctor, had moved, but her mother came back to Birmingham, six months pregnant, for the birth. 'I was conceived in New Zealand, so I should be eligible for New Zealand citizenship.' Her first marriage took place when she in her early twenties, to a teacher 20 years older, whose name she affects to have forgotten. She had a son, Nick, now aged 38. Then, in 1962, she married Ron Weldon, who sold old furniture in Chalk Farm, north London - very nice old furniture, for I once bought a pine table from him. He seemed the arty one, in those days, and Fay was the quiet little woman, giving birth in slow succession to three more sons.

She worked first in the Civil Service and then in advertising. It was only in 1967 that she produced her first novel, The Fat Woman's Joke. Since then, Fay Weldon novels have entered the language. Everyone knows her flavour, her obsession with the sex war, either from the books or their adaptations on television. The Life and Loves of a She-Devil, in book, television and film versions, earned her a small fortune. Now she earns an average of about pounds 200,000 per novel, which makes her about the best-paid literary novelist in the country.

Behind that Fay facade is a tough businesswoman, very professional, always half a dozen projects on the go, turning them in on time, making sure her agent gets the best possible deal. Jealous rivals say she is overpaid, and never earns her royalties, which is why she has changed publishers so often.

'I suppose I am a loss leader, but in the end my books usually sell out, if gently. Publishers never pay more than they can possibly help. They say oh, we'll have to pay you less, because otherwise we can't publish someone's first novel. I say they should carry the risk. That's their job. It's a commercial world, so you have to get the best deal you can. I see money as a spur to finish the work on time, not the reason for writing it. Otherwise I'd just sit around all day, chatting or watching television.'

Like most highly prolific writers, what you see is just part of the iceberg. She has many scripts still unmade, which probably never will be made, but she bashes on, then when suddenly several things come out at once, people say oh no, that Fay Weldon is everywhere. She's fairly fallow at the moment, though there's a new novel out in May (its title has changed three times, so no need to plug it) and a Radio 4 play in February, The Hole in the Top of the World, recorded in Hollywood, filled with Hollywood stars. Who says radio has no money? 'I did it earlier as a stage play, and no one understood it, even me.'

She works from 8am to 1pm every day, in pen and ink, then every five pages her secretary puts what has been written on the word processor, and Fay corrects it. Her first draft is done either in bed or sitting on the stairs. 'I like the stairs because I can think of the ghosts of all the people who've lived here . . .'

That's enough being Fay, thank you. What about your money? Long faces, big sighs. 'Big sums might go through my bank account, but they don't seem to stay there. I started life in debt and feel I still am. I'm neurotic about money. It gives me great stress, but then I love stress. People think stress is like the devil, out to get you. I thrive on it.'

She has been generous to her four sons when they have been in need. One moment she raves about them - their brilliance, their genius, their beauty, their incredible talent - the next she sighs and says they are all unemployable. Nick, the oldest, is married with two children. He got a first in philosophy at Keele then became a musician, currently teaching the piano to one of Melvyn Bragg's children. At the same time, he's just done a Prue Leith cookery course. 'He did it brilliantly, managing perfect Florentine cakes with 72 bubbles on the bottom. I think that's right.'

Dan, 27, is in films, currently working on a script with his mother. 'Did you know he won a prize at the Potsdam Film Festival? You may well ask what is the Potsdam Film Festival and I will say it is very important. His film was about Gabriel Garcia Marquez, which is interesting, as Dan seldom reads a book . . .'

Tom, 21, is a New Age traveller, out there somewhere. 'He's also a fire-eater and phenomenally good-looking. He was the one I worried about most. The others might have taken themselves to the brink of disaster, but always managed to pull back. Now I feel that Tom is old enough to know what he's doing and he does appear to be happy. I don't worry about them as I did. Perhaps the human mind can only stand so much worry.' Sam, 14, is still at school, fond of Spurs, but now even fonder of parties. So it goes.

'If I say they are unemployable, I mean it only in the sense that they would have difficulty with a 9 to 5 job, being told what to do by someone probably less intelligent than them. That's true about a lot of middle-class children today. I call it the open fridge policy - brought up allowed to go to the fridge when they are hungry. The alternative way is to sit them down to eat when you say so, to go to bed when you say so, to wear the clothes you say so. If you are accustomed to the open fridge life, you find it hard to adapt to hierarchies. No, I don't regret how I brought them up. Are they spoilt? What do you mean? I don't understand that word. If you live with your children, you love them, that's all there is to it.'

In London she has two small terrace houses side by side; one is occupied by her mother, while Fay lives and has her office in the other. She is about to buy another, bigger house, several streets away, to be her permanent home.

Her Somerset home, and her 30-year marriage, is over. She and Ron are now getting divorced. She was, apparently, barred from her marital home for a time and camped nearby, which was when the tabloids arrived, hoping for She- Devil headlines.

'You could say that my 'fame and success' did not help our marriage. All my youth I was terribly shy, very neurotic with no self- confidence, a pathetic specimen who thought herself stupid. I wasn't even made a prefect at school (South Hampstead High School for Girls), yet I had degree in economics and politics by the time I was 20 (from St Andrews). It's taken me years to have the confidence I now have. I realise my opinions are just as good as anyone else's.

'I can reproach bishops, go on television, make speeches and utter wild generalisations about the human condition, say the simple things that people think but don't say because they fear it's what six- year-olds might say. Such as, right, we have three million unemployed, while those in work are working harder than they have ever worked. So, why shouldn't everyone be in work, but only work half time, from 10 to 2? Wouldn't that be sensible?'

A man appeared behind her, then made himself some coffee in the kitchen. No, not one of her sons, she said. Your feller, then? 'I'm not saying. For all you know, he could be the plumber, couldn't he?'

Hmm, might this explain the glam hair-do and vampish expressions? Perhaps it was all lies about dressing up for our photographer.

Did she miss being married? 'I like marriage. Always have done. I hate being on my own. I like company and noise and things happening and endless chat. I might even have another child. Oh yes, you can. You go to Paris and there's a doctor who can render you pregnant at any age. If you have the money, there are doctors who will do anything for you. But perhaps not . . .

'I still have a lot of getting over to do. It's been very emotional. The agonising continues. Thirty years of marriage is a long time. I don't know how women of my age ever survive when it happens to them. Usually they have no income, no work, no family, no friends. I can see why they just curl up and die. I do feel exiled, punished in some way. I miss Somerset, not just the landscape, the place I had in it.

'At present, we are not in communication, but the divorce is going ahead. I'm told I could be liable to give him half my wealth and half my income from now on. Some days I wake up and I feel doomed to 10 years of hard labour just to pay for two households, then I think well, what else would I be doing if I wasn't working?

'The divorce law has been devised to protect wives who are not earning, and I am not quarrelling with the law. If it works to my detriment, as it obviously will because I have the bigger earning capacity, then that's my hard luck. It's already had one interesting effect on me. I now know what it's like to feel like a man . . .'

(Photograph omitted)