Over the years, Jane Asher's virtues have earned her considerably more scorn than her vices. Since she became a professional cake-maker, her profile has risen like a slightly oversweetened Victoria sponge. We see her on daytime television, demonstrating how embarrassingly simple it is to make sloe gin; we read her books on fancy dress (go on, it's easy - transform your daughter into a snowflake; send your son to a tea-party disguised as Thomas the Tank Engine); at supermarket check-outs she smiles down at us beatifically from the cover of housekeeping magazines, wielding a patchwork cushion she's made earlier (and which, incidentally, can be unravelled to form a handy little travelling quilt). Jane Asher has become a paragon of domestic virtue: beautiful, saintly, unassailably nice and - to those of us whose custard curdles even when it comes out of a packet labelled 'Bird's Eye' - exasperating, prim and utterly banal.

She arrives to meet me at the Conrad Hotel in Chelsea Harbour dressed in jeans and a white T-shirt, radiating good humour, and looking at least a decade younger than her age (she's 53). 'Sorry I was slightly delayed,' she says, apologising for the fact that she is three and a half minutes late. We are here to talk about her most recent book, Jane Asher's Tricks of the Trade, a compilation of household tips. Throughout the book's 316 pages, she answers inquiries on a myriad of domestic dilemmas, among them how to clean pillows filled with curled duck feathers, how to find replacement crystal stoppers for an Edwardian cruet and how to get the maximum usage out of a Hinari juice extractor. She appears to have an answer for everything. The only hint of her fallibility comes on page 134, when she is asked to suggest to what possible uses the fruit from a White Marseille fig tree could be put. 'OK,' she writes. 'I'm going to come clean. I had never heard of this fig. I was feeling very inadequate until I discovered that neither Prue Leith nor Sophie Grigson had heard of it either.' So we'll gloss over that.

I ask Jane Asher what it's like being a household goddess. 'I'm not,' she replies. 'That's just a label, it's nothing to do with reality. Things go wrong in my life like in anyone else's but I don't talk about that in public because I don't think that people want to know. I've become objective about myself as a brand - I can discuss Jane Asher without really thinking that it's me.'

The real Jane Asher was born in London in 1946, the second of three children. Her mother, Margaret, was a professor of classical music at the Guildhall School of Music and Drama; her father, Richard, a doctor. She made her first screen appearance aged five when she was cast in Mandy and, by the age of 15, had eight films, four plays, 100-odd radio broadcasts and nine television appearances to her credit. She was joined in these endeavours by her siblings - her brother, Peter, went on to become part of the Sixties pop duo Peter and Gordon. If child-stardom has its pitfalls, Jane is not the sort to dwell on them. 'I loved the theatre,' she says. 'I loved make-up and I loved showing off - it's a natural instinct in a child. The great thing about acting when you're very young is that as long as you say something reasonably well and look interested in what's going on, everyone thinks you're wonderful. It's only much later you realise how hard it is.' She coped admirably with the transition to adult roles and, during the Sixties, regularly cropped up in a number of plays and films such as The Greengage Summer, Alfie, Henry VIII and His Six Wives, Great Expectations, Romeo and Juliet and Brideshead Revisited. In 1970, briefly, she strutted the boards of Broadway when she was cast in The Philanthropist.

When she was 17, she met Paul McCartney. She was working for the Radio Times, reviewing a concert at the Royal Albert Hall; he cornered her in a corridor and (after a conversation during which they reportedly discussed gravy) decided she was 'a rave London bird'. They enjoyed a dignified courtship ('She's so nice,' McCartney explained, 'I haven't tried to grab her or anything like that'), during which Paul moved himself and his bass guitar into a garret room in the Ashers' family home in Wimpole Street. He later bought his own house in St John's Wood, north London, which Jane helped him to decorate. Her housekeeping skills were already beginning to surface: during a fit of spring cleaning, she once threw away some of the Beatles' early songs, mistaking them for scrap paper.

The relationship lasted five years, during which Jane and her family took McCartney on holidays and cultivated his interest in fine art (he acquired paintings by Ren* Magritte and a sculpture by Eduardo Paolozzi). Jane persuaded him to buy a farm in Scotland and the couple made a spiritual journey to the Maharishi's ashram at the foot of the Himalayas where they dabbled in transcendental meditation. Paul wrote a number of songs in her honour, most famously 'We Can Work It Out'. They didn't. The relationship ended abruptly in 1968 when Jane found Paul in bed with another girl. She has never spoken about him since. I ask her if she still listens to the Beatles. 'I'm sorry,' she says, her expression momentarily darkening, 'but that is the sort of question that I don't answer.'

In 1971 she married the cartoonist Gerald Scarfe, whom she met at a Private Eye party. They have three children - Katie, 25; Alexander, 16; and Rory, 14 - and live in a large and rather grand house in Chelsea overlooking the River Thames. 'All the children are living at home at the moment, which is lovely,' she says. 'There's nothing I like more than when we're all just there together on our own, being ordinary.' Asher's acting career began to slow down with motherhood ('I never wanted to be away from the children for long') and in the early Eighties she started to divest her domestic wisdom in a series of kitchen-shelf books - Jane Asher's Party Cakes, Silent Nights for You and Your Baby, Jane Asher's Fancy Dress and Easy Entertaining, to name but a few. They sold like sun-dried tomatoes and, in 1990, she set herself up with a bespoke cake shop in Chelsea.

For Jane and her trusty team of butter-icers, no commission is too daunting. 'People ask for the most curious cakes,' she says. 'We made one shaped like a ghastly pustule for a group of medics, and another like a human heart for a man about to go into hospital for a bypass.' She has also baked up Corinthian columns, football pitches, life-sized reclining nudes, and a quilted make-up bag - for Joanna Lumley. Earlier this year she started a mail-order line, dispatching ready-packaged party cakes around the globe, and she provides the individually portioned, sugary treats for the business and first-class passengers on British Airways. Her baking business has by no means impeded her extracurricular activities. Since opening her shop, she has presented a cooking programme on GMTV and four series of Good Living on the BBC; she has become the face of McVitie's biscuits; she has appeared in four plays; she has written ten books; she has meted out household tips in Jane Asher's Magazine (a check-out periodical in which the cover star was generally herself); she has regularly rattled a collection box for the National Autism Society, and she has celebrated her 50th birthday by posing for Esquire magazine dressed in nothing but a copy of The Times.

Is the real Jane Asher as capable as the brand name? 'No, of course not. I have help - I send my laundry away, and I have a housekeeper living in, so it is completely unfair to say that I am some sort of superwoman - my children laugh like drains when they hear me described like that. I'm just very lucky. The only housework I have to do is cooking for the family and sometimes I buy packaged food. I've nothing against it in principal other than the expense. Basically, I am a slob.' Other than secreting the odd ready-made kedgeree into the oven, how does her slobbiness manifest itself? 'I like watching afternoon films on the television. And I can't get anything done unless I am given a strict deadline.' Does she smile as much in private as she does in public?

'My world is not perfect,' she says. 'Because of baking cakes people think I'm a nice sort of fluffy thing, but obviously it's not as simple as that. No one's that simple. Like everyone else I know what it is to feel despair. After our first child was born I had a little hint of post-natal depression, which was interesting.'

A few years ago, Jane started writing novels that reveal a perception of the human condition which is unusually bleak. Her first two books, The Longing (1996) and The Question (1998), run through the gamut of human misery - bulimia, infertility, adultery, sexual obsession, revenge and madness. Her third, due to be published next spring, will tackle the issue of obesity. It's a far cry from Keep Your Baby Safe, Eats for Treats and the dozen other soothing titles listed in her Who's Who entry. 'It's not that there's a dark side of me bursting to get out,' she says. 'But I've glimpsed the other side of the coin. Everyone has.'

The most important influence on her writing was her father, an endocrinologist at Central Middlesex Hospital who identified MŸnchhausen's syndrome (an affliction which causes its sufferers to mimic other illnesses in order to draw attention to themselves and which was the subject of her first novel). 'It was typical of him to name it after Baron MŸnchhausen instead of himself,' she says. 'He was like that.' When Jane was in her early twenties, her father killed himself by taking an overdose of barbiturates. 'He was a very good writer,' she says. 'He was obsessed with using good English and not being pretentious. Sometimes if I find myself writing a long-winded passage, I can hear him saying, "Just put it simply; don't try to be clever."'

Jane Asher's most endearing quality is not her proficiency (in, it would seem, just about everything) but her vulnerability. She does not like talking about herself other than as a brand name, but, when she does, it is clear that her brain contains considerably less air than her sponge cakes. In 1987 she wrote an article about growing up for The Sunday Times in which she said that she worried about 'figures of death stalking my loved ones' and suffered 'deep, black holes full of inexplicable panic'. Does she still? 'I sometimes lie awake at night agonising about things,' she says, 'but they often seem less daunting in the morning. Having children makes you much more sensitive to the potential horrors of the world - it makes you realise the amount of pain you could be in for. I'm not very optimistic for the world as a whole.' Does she believe in God? 'No. I'm definitely Darwinian. I can't understand how there can be a God unless other things take the can for what goes wrong or unless he's a bastard. But I wouldn't want to crush anyone's belief - I might be totally wrong. I might get up there and find St Peter at the Pearly Gates and think, "Oh, damn."' If he's tried one of her plum puddings, St Peter will probably let her in.

From the November 8, 1999 edition of the Daily Telegraph