'How can you get into trouble for saying what is true?' Joan Collins talks man troubles, twerking and the problem with society today...

I meet Joan Collins in Claridge's, because, let's face it, where else do you meet this long-serving star of stage and screen and epitome of old Hollywood glamour, who has more recently branched out into books and one-woman shows and – wait for it – her own brand of wigs?

As I loiter in the lobby with my six-year-old daughter Lily, in Collins sweeps, looking sizzling in a leopard-print top and cream-coloured straw Stetson. She immediately leans down and shakes hands with Lily, and asks if she'd like to come and sit next to her and eat some ice-cream.

Collins and Claridge's go way back. She loves the hotel so much that she appeared in the recent BBC documentary series about it, and married her fifth husband, Percy, here in 2002. The staff flutter attentively and guide us to her usual table, tucked in a corner away from the gawpers.

Those who have met Collins tend to go on about how good she looks for her age – she turned 80 in May – and now I, too, can report that she does, up close, look sensational: all glittering eyes, burgundy lips and precipitous cheekbones. She's never had surgery as she's too phobic to go under the knife but she did once have Botox. "Never again," she says.

Lunch for Collins is a plate of sliced avocado and smoked salmon – she doesn't do bread, or the crème fraîche that comes on the side – and this, she tells me, is the secret of her youthful appearance.

"Avocados!" she cries. "You know, I really think I should do a commercial for avocados, as they are so good for the skin." Keeping trim requires effort, she says, "but I enjoy looking good. I mean, I exercise, but I'm no Jane Fonda. And I did very well in the genetic pool."

In the early 1990s, a few years after she'd retired from playing the dolled-up mega-bitch Alexis Carrington Colby on the TV series Dynasty (for which, at the time, she was the highest-paid woman on television), Collins complained to her agent Sue Mengers that she was swamped with requests to play identical parts. Mengers offered some advice. "She said, 'Oh Joanie, just let your hair go grey and get fat and then people will take you seriously.' Ha! Can you believe it? I told her to fuck off."

Collins is extremely good company, and uproariously funny. She tells me she makes a point of never speaking ill of her fellow performers, but through her Twitter account has made exceptions for Miley Cyrus – "I said, 'People who twerk look like a berk.' Well, they do!" – and the film actor Toby Stephens, whom she called "a cunt" for writing a newspaper article in which he recalled working as a student at a theatre where she was performing, and her "just wafting around the stage being Joan Collins".

Collins also dotes on young children (she has three grandchildren). This is just as well since, 20 minutes into our chat, she suddenly looks startled, fumbles around under the table and brings out a sticky, pink-splattered Chanel shoe. "I do believe dear Lily has dropped ice-cream in my shoe," she says. I babble my apologies but she doesn't mind a bit. "I'm used to it, darling," she tells Lily. "When I take [her youngest granddaughter] Ava Grace out in New York we have a foot-long hot dog and then a banana split. Have you ever had a banana split? No? You must!"

We discuss her various husbands and boyfriends, about whom she writes with eye- popping candour in her new book Passion for Life, which is brimful of pictures of Collins through the years. Along with Nicky Hilton, the American hotel heir – whom, we discover, liked to brag that he, his brother and his father had "a yard of cock" between them – she also details flings with Harry Belafonte (they kept it under wraps), Warren Beatty (who wore her out with the "endless bonking") and the property tycoon Bill Wiggins (who, to her disgust, subsequently sold a story to the papers which claimed that Collins was almost bald).

She also opens up about her marriages to the actor Maxwell Reed, who drugged and raped her on their first date; her fellow actor Anthony Newley, who was pathologically unfaithful; and the record-company impresario Ronald Kass, who developed cocaine and heroin addictions and left Collins in catastrophic debt.

Joan, I ask, are you about to get into trouble with your exes for spilling the beans? "I haven't so far," she replies airily. "And anyway, Bill Wiggins is going to love it; he adores publicity. But I thought very carefully about it; how can you get into trouble for saying what is true?"

While Collins has made some dubious choices when it comes to men, what is clear from her account is that she is a relentless grafter who has kept herself and her children afloat through some seriously tough times, and has refused to become the meek housewife that several of her husbands wished her to become ("I have never been the mousy, stand-two-paces-behind, obedient 'little woman' type," she says in her book).

It seems to me, I say, that you are a feminist. "I think I probably am," she replies, "at least if it means when a woman is exactly equal to a man except physically. But wanting to cover oneself in jewels or couture or make-up and cherish being a woman, I don't think there's anything wrong with that either. We should celebrate being women and having the opportunities to do things that our mothers and grandmothers were not allowed to do. They were expected to stay at home and do the cooking and the cleaning. Though of course now we're expected to do the cooking and the cleaning and the working."

She is appalled at the pressures on young women today to have to look a certain way – "and I understand young men today don't expect women to have body hair anywhere. Even" – she points south – "down there. Ridiculous! Young women have been given an expectation of Barbie-doll beauty that doesn't exist in real life."

Collins also writes for the first time about her current husband, the theatre producer Percy Gibson, whom she remains dotty about. The couple met when she was performing in the AR Gurney two-hander Love Letters in the US in 2001. As was widely remarked upon when they announced their engagement, Percy is 32 years her junior. "If he dies, he dies," Collins quipped at the time.

Five husbands in, she still rates marriage very highly. "It is," she explains, "the definitive commitment – says she who has been married five times! But I do think it's very important, if you're going to spend the rest of your life with somebody, to know that you really like them. Because when the pheromones wear off, which of course they will, you have to have a strong basis. Tell me, Fiona, do you have that with your husband?"

We can just about stand to be in the same room, I say.

"Well, there you go," she smiles. "Friendship is the key. What a shame it took me so long to work that out!"

Born in 1933, Collins is the daughter of a theatre-agent father and a mother who was a champion ballroom dancer before she gave it all up to be a housewife. Her grandmother had been a dancer and actress in the early 20th century. When Joan was five, her grandmother hitched up her skirts in the family living-room and showed her granddaughter how to do the splits. (Joan copied her and, with a bit of limbering up, can still do them now.)

Collins' father encouraged her to pursue acting and told her: "Don't ever ask or depend on anyone for anything." He also warned: "You better make all the money you can when you're young because by the time you're 23, you'll be all washed up." Happily, she would put him right on that one.

Collins' first paid work arrived when she was 16 and a student at Rada. "A photographer came in and wanted to see 10 of what were considered to be the prettiest girls in the school. We all lined up in front of him; he chose a couple of us and one of them was me. I went the following week to a freezing studio and they made me put on a blue bathing suit and lie on a cold floor with fake sand and took a picture of me for the cover k of a magazine called Good Taste. I looked like a drowned rat. I think I got paid 30 shillings."

She was soon picked up by the J Arthur Rank Film Company, which billed her as the British Elizabeth Taylor. She would go on to star in a succession of films that veered from the not-bad (1956's The Opposite Sex) to the so-bad-it's-good (1977's Empire of the Ants, now deemed a cult classic).

Her career had tremendous peaks and troughs, and it was a particularly grim trough in the 1970s that prompted her to take the lead in the soft-porn film of her sister Jackie Collins' book The Stud (1978). The similarly raunchy The Bitch followed the next year, after which Collins' career was firmly back on track and she landed the role of a lifetime in Dynasty, in 1981.

Over the past 20 years, Collins has expanded beyond acting and become quite the entrepreneur. Since the early 1990s she has churned out scores of books, from memoirs to novels to beauty guides and, most controversially, an irritable manifesto on the modern world published last year.

The World According to Joan caused a particular stir since, along with providing assorted beauty tips, it castigated feckless parents, spoilt children, yob culture, the death of chivalry and the obese (whom she called "Jello warriors" from "Planet Girth"). "Yes, it did cause a bit of a fuss but I also had an enormous number of people write to say, 'Oh my God, that's exactly how I feel but I've been scared to say it.' The leftie newspapers weren't so impressed. Haha!"

In her 1980s heyday, Collins was a well-known defender of Margaret Thatcher and Ronald Reagan. When she attended Thatcher's funeral, she was furious to see protesters outside. Would she still describe herself as right-wing? "I wouldn't say right-wing, no," she says cautiously. "I'm more a middle-of-the-roader. Percy had a good expression for it. I'm a humanist."

When I ask her her views on the current government, she looks pained and says, "Oh please, don't get me on politics. I'm always being told that I'm blunt and opinionated and I talk too much. Someone once said to me, 'Actresses shouldn't talk about politics, they're not politicians,' and I think they're right. But I'll say this: I think they're doing the best that they can."

Along with the books, there have been TV cameos, her touring one-woman show called An Evening with Joan Collins and adverts for everything from cosmetics to chocolate bars. She has just completed voice-over work on a children's movie, Saving Santa, alongside Martin Freeman, which is due for release this Christmas. And now her latest wheeze: wigs.

"I have designed my own collection and they are fabulous," Collins beams. "It was Percy's idea. All of them are named after someone very important in my life, whether it's a fictional character or my family or friends. Each has a name that is meaningful. The redhead is Arlene, after my dear friend [the actress] Arlene Dahl."

It's these various money-making schemes, combined with her relentless energy, that allows Collins to maintain homes in London, Los Angeles, New York and the south of France.

She insists that, at 80, there's no chance of her slowing down and taking life easy. Yet her favourite place in the world, she tells me, is her house in a small village just outside Saint-Tropez. "It's my bolthole, a place to go after the insanity of going from country to country. Percy and I will go for lunch and to dinner or just sit on the beach. Sometimes I'll stay there for 10 days at a time and I just don't go out." For a moment, Collins comes over all misty-eyed. "For me, the best thing in the world is just to sit there and look at the view."

'Passion for Life' by Joan Collins is published by Constable, priced £25