Her first love may be the stage, but it's as the high-octane star of The Colbys and Dynasty that Stephanie Beacham is best known and loved. Now she's back in character, in a new series of Bad Girls.

The actress Stephanie Beacham has a home in Los Angeles, a beachhouse in Malibu to house her two-year-old grandson's bucket and spade and a London base she thinks is simply perfect. The London base is the tiniest of one-up, one-down houses in an unpromising Bayswater side street off a side street off a side street. When I arrive, I can hear jokes and giggles from upstairs where she is closeted with the photographer and his assistant, so I go and put my head above the bannister, just to say hello, and what I see makes me laugh quite a lot.

The performance that is going on in her bedroom is very full-on Hollywood for such a tiny venue. Stephanie Beacham is kneeling on her bed in a virginal circle of carefully arranged white skirt, giving it lots of teeth, eyes and cleavage and looking spectacularly glamorous, very film-star and very mischievous. "We don't talk about age," she says demurely, later, but she's mid-fifties and looks fabulous in an annoyingly natural way. No question of being passed over for glamour roles yet, and it's a very pleasing irony that her grandson's name for her, innocent, unprompted, is "Glama".

Stephanie Beacham's recent appearances on British television have been in perfect line with this side of her persona - the Graham Norton show, an inevitable member of the list of TV superbitches of all time for her role in The Colbys and as Joan Collins's sparring partner in Dynasty. But she's coming back to a rather less glamorous venue: Larkhall prison in the drama-a-minute series Bad Girls. Carrying the baggage she does, she's appearing, with Amanda Barrie, as one of a pair of Costa del Crime time-share conwomen. It's all part of an overall view of her life and career that means she knew it was time to do British television. Television gives her the visibility to attract the badly paid, chewy theatre roles she really loves doing, and Hollywood gives her the money to maintain the lifestyle to which she wants to remain accustomed Steffie, the down-to-earth British actress, knows that she depends on Stephanie Beacham, the international player, to keep this going. Steffie and Stephanie Beacham look after each other very well.

Knowing The Independent was coming, she was prepared to give us Steffie, curled up modestly on her tiny sofa in her tiny sitting-room as befits a veteran of the English stage, single mother and besotted grandmother, but it seems Stephanie Beacham in capitals is what is wanted and Stephanie Beacham in her full, self-aware kilowattage is what the photographer gets.

She is quite clear about where one stops and the other begins. Steffie makes sure that Stephanie is properly groomed, dressed, rested and lit - and talks about her cheerfully as "she". "When she became so commercial I had to protect her," she explains. "She is a product." It's Stephanie Beacham who needs good lighting, proper make-up and, at certain points in her career, the bad-guy heavies who would protect her from public attention on the streets, in stores. That was when she was the superbitch star of The Colbys and Dynasty, a sparring partner for that other superbitch and national treasure, Joan Collins.

Stephanie's family, her two daughters by her former husband, the actor John McEnery, have found that Stephanie Beacham, superbitch, is quite handy to have around. There was one holiday when they had a problem getting their skis on a plane. "Oh, come on," said the daughters, "just be Her." So Stephanie Beacham, down-to-earth mother and self-deprecating British trooper, said oh, all right then; and Stephanie Beacham, star, switched on the light, and the skis got on the plane.

This sort of behaviour wouldn't go down well in Birmingham, which is where she was very content to earn peanuts last summer doing "the best work of my life" as Elizabeth 1 in Elizabeth Rex at the Birmingham Playhouse. "Come and see," she says, jumping up and taking me into her minute kitchen to look at the poster. No keylights and kind make-up artists here. Just an actress sacrificing all vanity to a white mask, bald head and the looks appropriate to a 67-year-old woman on the eve of her lover's execution.

"I think that was the best piece of work I've ever done," she says eagerly. "I don't need to look pretty but I don't often get the opportunity. One thing I know is that you can elongate your shelf-life enormously if you play older than your self. There is supposedly a gap for actresses. They say you get no work after 40 and I nearly bought into it for a while. If you're told something enough times you believe it, but I think it's important to look at what we accept as the truth and change it."

Stephanie Beacham has had a lot of practice at challenging the accepted view of how things should be. Two key things about her are that she was born beautiful and that she was also born partially deaf. Another key thing is that she was born after the Second World War to the sort of encouraging parents who radiated the stiff-upper-lip, just-get-on-with-it-old-girl approach to life of the war generation so that the deafness was never seen as an obstacle, not even, once it was accepted as incurable, mentioned. Just not a problem. It wasn't until she was already a student at Rada that she saw a specialist who told her that her deafness was so profound that she'd never be able to be an actress. That simply made her try harder to be the best actress in her year, and later she met another specialist who helped her devise coping strategies and protect what hearing she had. She doesn't spell this out, but the inner determination to succeed despite her deafness helped her develop habits of independent thinking and the need for the solitude that helps you sort things out for yourself.

"I was incredibly lucky. I was brought up to know that, whatever I chose, I'd be a huge success. That was a gift from my mother. Parents now think they have to take children to everything, but I was wandering the streets five times a week going to my ballet classes. When I did encounter someone who opened his raincoat and I told my mother, she just said, 'well, you'd better take a different route, dear'. We were less protected but we had more freedom; I was able to cycle without a helmet and feel the wind in my hair. I could leave our house in New Barnet with a few provisions, very Milly-Molly-Mandy. Wandering alone, that was when I'd do my Pooh Bear hum, that was when you noticed the light in the trees. At school I'd think, I've got to be by myself now. I needed it; because of my hearing I'd get tired. I'd go to the library and enjoy the smell of books and stare at the stuffed birds. A lot of my downtime wasn't downtime at all."

She could have got away with an awful lot, but the deafness was never given as an excuse. At Rada she absolutely knew that she was going to make a career in French films and Shakespeare. "If someone had told me I'd make a career in soap opera in California I'd have cut them dead. What I had wasn't cockiness, it was an innate confidence, that was my greatest blessing. I knew never to look sideways, just look to where you want to go. It was all like butter. Just lovely, everything came."

So, no arthouse movies but heaving bosoms in titles like Super Bitch, Horror Planet and Dracula AD72, which subsidised a rather distinguished theatre career - Wilde, Shakespeare, Pinter, Ibsen, Strindberg, Shaw. The young Stephanie Beacham learnt tips from Ava Gardner on how to look good on screen - tilt your face up, keep your hands up to drain the veins and make them look younger, follow the key light. 'The young Stephanie Beacham, at 22, co-starred with Marlon Brando in Michael Winner's The Nightcomers, a "prequel" to Henry James's Turn of the Screw. Marlon became a life-long friend They went for a pre-shooting dinner with Brando, Winner and the censor, John Trevelyan. Trevelyan cut across young Beacham's conversation and as she blushed in humiliation, "I felt a great, thick, fat hand come out and hold mine. If Marlon knew you were in discomfort he'd be wonderful, he had such sensitivity. We've stayed friends but it's a friend who's a wild bear in the forest."

Sometimes he comes out of the forest, like the time the forest fires raged near her home and be called at 2am to offer shelter to her and her house guests. "That's cool," she says conspiratorially, glowing with retrospective delight. But she didn't go. It was more important to her to stay with her own home. I think that's cool too. Stephanie Beacham is her own woman and she was at 22. She was blacklisted after Nightcomers when she walked out on the producers who wanted her to pose for Playboy. "You're dead if you walk out," they said "Ever seen a skeleton walking?" she said, turning on her heel. It was back to Britain, to learning her craft and to marrying, having babies, becoming a single mother. Art struggled with the cost of living. "One year I did six new plays, Greenwich, The Royal Court, Hampstead, and I earned £2,000. I realised I needed money. I went back to Hollywood in 1985. I went for The Colbys and then to Dynasty to fight it out with Joan. It was blissfully silly."

And surreally glamorous. She got used to the personal trailer, the bodyguards in malls, the legendary co-stars, like Barbara Stanwyck and Charlton Heston. She laughs at the dreamlike experience of protecting her Malibu house - the last one, the big one - against rising floods, floundering about with Dustin and Goldie, Jack Lemmon and Sylvester Stallone, all of them hauling their own sandbags. There was a point where she addressed her King Charles spaniel over the dog food and told him it was absurd that her lifestyle was so expensive that she had to earn a quarter of a million a year before either of them could eat. It's scaled down a bit now. The new beach house is much smaller, and it's there to house the bucket and spade and tricycle.

She was thrilled that Amanda Barrie, her partner in crime in Bad Girls, was booked to play a genie in panto, freeing her up to whizz off to LA and be a granny over Christmas. For Stephanie Beacham, superbitch, grandchildren are the new rock'n'roll. She's avoided re-marriage for years. "I realised I could do two of the three things - mother, wife, actress, but not all three. I had a blessed and gorgeous series of boyfriends over the years, several four-year relationships. They didn't last because I knew they were the third priority after my children and career. I had a high libido and I liked having a handsome young man around but now I've got no room. I don't care. I'm too used to being alone. There's been a definite change since Jude came along. It's as if having a grandson fills up your love bags, like a second helping of pudding on a cold day. It hit me a bit sideways. I'd set myself up as a free agent and suddenly I'm a granny. Most of my life I've not felt complete without a handsome young man at my feet. Now I still have one, but I have to pick up his toys. It's a most delightful thing."

It's because of two-year-old Jude that home is still Los Angeles and Britain is where she comes to work. But it's also were she comes to ground herself, abandoning the personal trailer and the expert lighting technicians for the grittier experience of work for the work's sake. "This is where the earth is," she says. And her feet are firmly on it.

The first episode of the new series of 'Bad Girls' will be shown on 8 May at 9pm on ITV1. Stephanie Beacham joins the cast in episode three, to be broadcast on 22 May