Gossip columns are bewitched by the cult of the cougar: the alluring, predatory older woman who unashamedly revels in her sexual prime.

For all its playful intention, there seems something rather insulting in this fascination, not least the judgment that lies at its heart. But none of this fazes the perpetually glamorous, 63-year-old Stephanie Beacham.

“Cougar? I think I probably invented the lifestyle before I ever heard the term!” she laughs, alluding to her past form dating younger men.

“I think that’s as near to a comment as I can make. But I don’t know … God bless us all for living as vivid lives as we can – we’re going to be spending long enough in boxes at the end of it all.”

Always sporting in sending up a public image forged on 1980s primetime TV as Dynasty’s devious Sable Colby, Beacham is probably able to laugh at herself because she’s made plenty of roles her own since the days of shoulder-pads and ozone-depleting, anti-gravity hair. From Bad Girls to Coronation Street, via a turn on the late Celebrity Big Brother, Beacham says she’s been “extraordinarily lucky”

in the opportunities she’s been given and actually squeaks with excitement at the thought of playing opera icon Maria Callas in Master Class.

“This is a really big thing for me. The amount of work that goes into it is very daunting, but it’s such a moving story. I’ve played so many divas and bitches and loved every one of them, but Callas has a soul that goes all the way through.”

Terence McNally’s play finds Callas in her caustic later years as she tutors a group of New York students, both her heart and voice broken beyond repair through overwork at the start of her career and her doomed romance with Aristotle Onassis.

“She was a celebrity in a very modern sense in that she encouraged it but was ultimately eaten by it,” Beacham says.

“In the play, she explains that she knew she needed a look and she got one. And when you think of her you can picture the beehived hair, the thick eyeliner. But one of the most moving things about her story was that her coffin was apparently pushed aside during her funeral so the paparazzi could take photographs of the people who attended.”

We’ve heard all too many stories of the corrosive effects of fame since Callas’s death at 53 of course, and Beacham says she can see why that should be.

“I think some people suffer from a sort of claustrophobia, and don’t quite get that fame is … how shall I say? Cyclical. I think I’ve been famous about three times, if you see what I mean, and I know the joy of having my own quiet time. But I think Maria went into her last years not feeling at all satisfied – she had lost her voice and the love of her life.”

Born in Barnet (a location she swapped for the more glamorous Casablanca in early interviews), Beacham was diagnosed with total deafness in one ear shortly after birth, and laughs that Master Class is mercifully free from any operatic singing demands. After a brief career in modelling and parts in TV series such as The Saint and Jason King, she made her cinematic debut alongside Marlon Brando in Michael Winner’s steamy The Nightcomers in 1971.

“Marlon was a great friend and a one-off, but the person who was my real partner for so long was Charlton Heston [with whom Beacham worked on Dynasty spin-off series The Colbys].

“He was reliable and beautiful and a wonderful friend. It moved me enormously when he phoned me after he’d been diagnosed with Alzheimer’s and said ‘My dear, before I forget, I wanted to tell you that I love you…’” Relating this story with a barely perceptible crack in her voice, Beacham says she’s been fortunate in working with some of the greats, but is equally quick to sing the praises of a rather less critically-acclaimed screen presence. It’s hard to picture Coronation Street’s Ken Barlow descending from a Technicolor Mount Sinai bearing the Ten Commandments hewn in stone, but Beacham says Bill Roache deserves recognition as “one of the greats” after her guest slot as Barlow’s sultry love interest.

“There’s a strange snobbery about Hollywood versus television and soaps, which is something I’d like to trample on. Bill has qualities of such kindness and enthusiasm for his work and getting it right. He had such dignity when his wife died [Roache’s wife Sara had a suspected heart attack during Beacham’s time on the show] and I can’t say too much good about him.”

Last year’s stint in Weatherfield was followed up with that most risky of career turns; a spell in Celebrity Big Brother purgatory.

Newspaper columnists marvelled at the way Beacham managed to maintain much of her dignity and poise against a backdrop of trying circumstances (including being caked on the head and enduring maligned cheap acrylic bedsheets). She even delivered a rather Shakespearean lament as the housemates prepared for yet another humiliating task. “But are we whores or fools?” she asked, as Dane Bowers from Another Level and Vinnie Jones looked on, confused.

“It’s very intense when you’re in there and not everyone’s there to be friendly, but I can only say how much I enjoyed dropping the vanity and actually existing as myself.

“I was really proud to be the last woman standing [Beacham finished fifth]. There was a very strange moment when I was getting ready to leave, and I was sitting on the floor in the loo – one of the only places with any privacy – back-combing my hair. Showbusiness is very different from how anybody expects it to be [laughs].”

After the antics of Big Brother, Beacham “escaped” for a while, spending time with her partner – “a gorgeous doctor who lives in Spain” – and taking the time to decompress. She says it’s all part of looking after herself from a psychological point of view, but it’s hard not to notice she seems to look after herself rather well from a physical perspective too. How does she manage to stay looking so very good?

“I think it’s about the simple things,” she says, laughing off the question.

“Women have to lift weights and things like that in order to keep their bones strong, but I don’t make too much of an effort with that. The nearest I get is carrying shopping. But I do keep up with my yoga and Pilates, and you really are what you eat.

“But I tell you, if anyone’s got any good ideas about how to join up the synapses in the brain, I’ll take them. I need more of a mind than I seem to have, and this role is as challenging as anything I’ve ever thought of doing.”

Aside from the emotional rigour of playing the archetypal artistic martyr, there are the physical demands of the touring lifestyle (the play, directed by Chichester Festival Theatre luminary Jonathan Church, also reaches Theatre Royal Brighton in the new year). Beacham keeps up with her partner and loved ones via Skype and phone, but admits the transient nature of touring can be disorienting.

“It’s an extraordinary thing to open somewhere on a Monday night, then some time after midnight you land up at a strange place, probably without water, tea or coffee, and you’re very lucky to have taken a bunch flowers with you. You suddenly have to make that home. And just as you feel like you’ve lived there forever, you have to get out.”

She intends to devote some space in her long talked-of autobiography to touring, something she feels “doesn’t get the respect it deserves” in the industry. Progress on the book is slow, she says, not least because she’s very much entangled in the life of Maria Callas right now. At one point in our chat, I ask about our modern understanding of a diva, with it’s connotations of brattishness and puppies in dressing rooms.

“I think a lot of that kind of behaviour comes from an insecurity, which is certainly what she had,” she says.

“But with her it wasn’t simply vacuous diva behaviour, because the standards she demanded of herself were very high … But while we’re on the subject, what’s wrong with puppies in dressing rooms?”