"I think you have to relax about ageing," Felicity Kendal purrs. "What else can you do?" Curled up on the sofa in the library of a London hotel, she looks ridiculously girlish in jeans, a black shirt and orange jumper. Her hair is dyed that expensive shade of honey and she is wearing tons of gold jewellery. She also has the tiniest thighs I have ever seen.

Women don't automatically warm to Kendal. There's something about that frisky sex-kitten persona that sets your teeth on edge. She's been voted Rear of the Year. She posed naked for Esquire in her fifties. And men - of all ages - go gaga at her name. Before our interview, I met a photographer who told me his assistant had left their shoot chanting, "Felicity, Felicity, you fill me with electricity." Hmm.

But then I read her 1998 autobiography, White Cargo, and completely changed my mind. It's a wonderfully funny picaresque account of her early life spent touring India and the Far East with her parents' Shakespearian theatre company. Kendal is quite merciless when it comes to documenting her own adolescent selfishness and ego. "I set out quite deliberately to be as honest as I could. If I was writing about something, I wanted it to be what I thought, not what I thought people wanted to hear."

The other surprising thing is that she was a complete tomboy. Her sister Jennifer, 13 years older, was the beauty. Felicity, nicknamed "Fatty Foo ", was the comedian. "My impression as a young person was that my mother was very beautiful," she says. "And my sister was absolutely smashing, and I was sort of not-so smashing. Having these two beautiful leading ladies in the family, it never occurred to me that I'd be anything other than a character actress."

She was thrown on stage at the age of nine in her father's production of Macbeth. Touring meant she had to attend dozens of new schools a year. " I constantly resembled Alice in Wonderland," she recalls in White Cargo of her many ill-fitting uniforms, with "blazers down to my knees over a skirt that showed my knickers. And it certainly did not help my concentration to think that I looked like a fat bag lady beside the delicate, wealthy and beautifully groomed girls of the convents."

When she told her actor-manager father that she intended to leave India to try her luck as an actress in England, he was not encouraging. "You stupid little bugger," he said. "They won't appreciate you." In fact, when she first arrived in London in 1965, she was turned down by everyone. Half-feral, badly educated and dressed in flamboyant, sequinned outfits, it's not surprising she failed to impress the black-polo-neck brigade.

For several years she tended to be cast in Asian parts because of her tanned skin and dark hair. But she slogged away and finally got a TV play called The Mayfly and the Frog, a two-hander with John Gielgud, who became an early champion. Kendal played the girl on the motorbike (she dyed her hair blonde) to his eccentric millionaire. Later she was offered a role as a lesbian in a West End play where she had to wrestle actress Tessa Wyatt in a bikini - the play was a flop, but won her good reviews.

She joined the profit-share Actors' Company, which included a young Ian McKellen. Finally she was cast in Alan Ayckbourn's The Norman Conquests (1974) with Penelope Keith, which became a West End hit. One night Richard Briers, an established star, popped his head round the door and mentioned a little TV series he'd been offered about a suburban couple determined to lead a life of self-sufficiency. Would she be interested in auditioning for the role of his wife? The rest is history.

Although it ran for only two years, episodes of The Good Life are still being shown 30 years later. And many millions of men fell in love with Felicity. Even the American film star Billy Bob Thornton has admitted: " We would sit there and drool over Felicity Kendal. It was her amazing voice and those tight trousers."

"It was naughty but wholesome," Kendal recalls. "Tom and Barbara were always dashing off to bed, but you didn't see them share anything more than a chaste kiss." This was the mid-1970s, after all, when women weren't even supposed to get drunk. "There was an episode in which the boys got plastered and Penny [Penelope Keith] and I said, 'We should get pissed as well.' But the BBC was really worried about it. It had to be sanctioned by the boss."

Although it made her Britain's sweetheart f (she was awarded a CBE in 1995), Kendal's role as Barbara - loyal to the point of lunacy - alienated feminists who preferred ballsy Margo to compliant Barbara. "She really used to irritate the Julie Burchills of the era," laughs Kendal. " They didn't like the way Tom dominated her."

Maybe we just didn't get the irony. Kendal's personal life at the time couldn't have been more different. After a painful divorce from her first husband, the actor Drewe Henley (they married when she was 20; her son Charley was born two years later), she became a single mother. "I discovered that I was able to flirt my way into almost any pair of arms I wanted," she writes in White Cargo. "For the next 10 years I was never without a love affair, never alone, never single. The good life image of the nice girl-next-door was indeed just an image."

After four seasons of The Good Life, Kendal was offered two TV series specially written for her. In Carla Lane's Solo she played a vulnerable but independent 30-year-old woman who throws out her faithless boyfriend and gives up her job. In The Mistress she was a florist trying to cope with the guilt involved in carrying on an affair with a married man. Some critics hated The Mistress. How could lovely Felicity Kendal know anything about adultery? Others thought it perfect typecasting.

In fact the red-tops have been almost pathologically obsessed with Kendal's love life since she left her second husband, the Texan-born theatre director Michael Rudman (they are now happily back together again). They married in 1981, and had a child, Jacob, who's now 17, but eight years later she left Rudman for the playwright Tom Stoppard. Stoppard then separated from his wife Miriam and Kendal became the Scarlet Woman.

She kept her head down and kept working, appearing in The Camomile Lawn (1992) and the sitcom Honey for Tea (1994). But arguably in the past few years her most impressive performances have been on stage. She and Frances de la Tour made superbly elegant drunks in Noel Coward's Fallen Angels.

On stage she can lay the ghost of Barbara Good to rest. Quite often she doesn't even look like Felicity. "It's an old-fashioned idea now but in the old days actors looked different in every part. You can act beautiful, like you can act crazy or sad. It's all part of the job. When I arrived you would have Maggie Smith playing something really funny, I mean she always looked amazing, but she wasn't a great beauty, and neither was Peggy Ashcroft, but then when they were playing beautiful women, they were stunning."

The running joke in Humble Boy was that her character Flora had had a nose job. "I felt I understood Flora," she laughs. "And I think many other women would understand her. She is a woman who always thought she would be more than she turned out to be. Every woman has those emotions, the feeling you might have missed the boat. So many roles for women demand that you make the audience fall in love with you but Flora wasn't written like that."

She and Rudman reunited in 1999, a year after her relationship with Stoppard ended. "There wasn't really a moment when we decided that we were getting back together," she has said. "We sort of slid into it." They have not remarried, she jokes, because with four marriages between them, they haven't turned out to be very good at it.

And independence is important. "My security is in my family, not in a house. The only time I ever feel nervous is when it's to do with my family. Having said that, I would feel terribly trapped if someone said, 'You're going to live in this one house for the rest of your life and do this particular, wonderful job and take wonderful holidays on this and that date.' I like change. My claustrophobia would be sameness."

THERE ARE many reasons to like Kendal. She's brought up two sons as a single mother. She doesn't lie about her age (58). And she enjoys being a grandmother (her older son Charley, 37, has two daughters). Yes it's sickening how good she looks, but she works at it (hours of yoga a day). And you sense she's a woman's woman.

It's ironic that after 30 years of trying to escape her sitcom persona, Kendal is doing another one. We're here to discuss a new series of the gardening and murder mystery, Rosemary & Thyme, in which she stars with Pam Ferris.

It's easy to mock the show (French and Saunders did a famous spoof) but it attracts nine million viewers per episode. When I ask Kendal why she and Ferris wanted to do something so cosy, she replies: "One of the things that appealed to me is that it's like a buddy movie for women. It's not a sleuth and a sidekick - they're absolutely equal. It's a slightly duller version of Cagney & Lacey. The other thing I like is it's totally unpretentious."

Kendal is no snob - if playing a telly role can bring people into the theatre, fantastic. She tells a story about playing Winnie, the half-buried heroine of Samuel Beckett's Happy Days last year: "We opened in Bath, and because I was in it and it was called Happy Days, most people hadn't a clue it was a Beckett play. On opening night you could feel the audience going, 'What? What are you doing?'"

"Then we opened at the Arts Theatre in London and something great happened. Quite often there would be young people, or a middle-aged couple standing outside, saying, 'We always come to see you in the West End or when we're over from America. We had no idea what this would be like, but we loved it.' So in that sense it was a great crossover."

The critics agreed. As Paul Taylor, The Independent's theatre critic, wrote: "In her very moving performance, Kendal allows you to hear the gasping panic under Winnie's bright protestations, and to see the emotional cost of continually having to heave herself back into a mode of ladylike graciousness."

It could be a description of Kendal herself, because there has been real tragedy in her life. Her first husband was diagnosed as manic-depressive and sectioned. Her adored sister Jennifer died of stomach cancer aged 50. Then for six years her father lay in a coma before he died. White Cargo was composed by his bedside.

"I wouldn't say it was a gift exactly, but I'm very glad I wrote it," she reveals. "It was a way of recording a very unusual period of history full of these extraordinary characters. My father did write an autobiography but it was slightly sanitised by my mother, so it wasn't quite the full-blooded story."

The book ends pretty much after the success of The Good Life. "I really wanted to stop it when I first came to London - my publishers didn't agree - because that was where 'she' stopped and I started. People say, 'C'mon now, let's have the next bit', but it's just not interesting."

Work has always been the driving force for Kendal. In White Cargo she writes movingly about the difficulties she and her first husband faced trying to maintain two parallel careers. Do actors have a selfish gene? "In any artistic job, like ours, there isn't a mathematical equation at the end saying, 'you've got this right therefore go up four paces', and there is no real definition - it's just taste, it's critical acclaim, whether you're fashionable ... all of that goes into it. So you have to do it for yourself, I think. But as you get older the choices are easier. You're not so torn by ambition and fear."

Increasingly, she says, she enjoys the role of Jewish matriarch (she converted in the 1980s when she met Rudman). "I find I want to be around my family more. At the moment Big Son [Jacob] is doing his A levels so I certainly won't be doing any theatre until later in the year."

How amazing to have a sex kitten for a mother. Does he enjoy her fame? " Noooo," she hoots. "He has these poker parties at our house where they all wear sunglasses, but I'm forbidden to speak to his friends. I bustle in saying [she affects a cut-glass accent], 'Would you like some popcorn?' and I can see I have absolutely ruined his cool."

The new series of 'Rosemary & Thyme' starts on ITV1 on 28 January