So, where does Samantha Jones end and Kim Cattrall start? Has the 53-year old actress ever felt herself blurring into the vivacious, voracious character she has played, on and off, for more than a decade? "No. Never. It's such a clear definition," she shakes her head. "Totally clear. It ends when they say 'cut!'" Really? To the casual observer, there have been plenty of times since Sex and the City exploded all over our screens in 1998 when it has been tricky to draw a line between the actress and the fictional Manhattan man-eater.
As Samantha sauce-potted her way around New York, bedding toy-boy models and millionaire executives, dispensing X-rated advice over brunch and, as a naked human sushi platter in one of the movie's funniest scenes, "getting wasabi in places you should never get wasabi," Kim was busily racking up her own column inches. There are her three marriages, the book, Satisfaction: The Art of the Female Orgasm, she wrote with her third, now ex-, husband Mark Levinson and her latest, now defunct, relationship with Alan Wyse, a chef 20 years her junior. Then there are other appearances which deliberately play on her glamazon/siren image: the Nissan advert banned in New Zealand for being too risqué ("I've just had the ride of my life..."); a television documentary, Sexual Intelligence, which saw her dancing with glee on the 26ft phallus of the Cerne Abbas giant; her semi-naked publicity campaign to save Diana and Actaeon for the nation (cue "Nice Titians, Kim" headlines); and, my favourite, her guest spot on Sesame Street where she proclaimed the "word on the street" to be (what else?) "fabulous". So Samantha, darling.
There's a hint of Samantha, too about her upcoming film roles – as the formidable PA (and mistress) to the prime minister in the Robert Harris thriller The Ghost and as a fading glamour girl in Meet Monica Velour. First, though, is a run on the West End stage as fiery divorcee Amanda in Private Lives. Given the hysteria which tracks her every step in Manhattan, I wonder whether she's experiencing a similar reaction over here. "I don't really feel like they're reacting to me because they don't know who I am," she corrects me, stiffly. "They're reacting to projected images, and my work – not to me. It's a little overwhelming. The thing I really love about London is that I can merge a bit".
Sex and the City's most out-there character, it seems, prefers to blend in. She politely refuses when fans ask to take her photograph – "I just sort of need time off" – and takes her privacy very seriously indeed. Even her stint on the BBC's Who Do You Think You Are?, which encourages celebrities to dig around for skeletons in the family closet, was a masterclass in revealing a little, while concealing a whole lot more. We learned plenty about the (admittedly explosive) story of her bigamist grandfather but not a jot about day-to-day life chez Cattrall. In the flesh, she's (if you were being kind) dreamy and vague, perhaps (if you weren't) a little stand-offish and evasive. A simple question about where she lives gets the gnomic answer. "Right now, it's London. It is where it is." OK, but does she own a house? "The property that I own is in New York. But I feel at home here now."
The thing is, Cattrall is a consummate professional. You won't catch her knocking fame or the paparazzi. "Like a fly in summer," she bats the air with her hand. "What you gonna do? I just deal with it." It's all part of the job and for Cattrall, acting is just that. The endless reports of bitching on the Sex and the City set? "A terrific waste of time. You've got eight pages of dialogue – get on with it. We all really, really like each other so if we don't see each other for a while, it's ok. It's sort of like a family. I don't speak to my brother every week – doesn't mean I don't love him." The troubled private life of Roman Polanski? (the director of The Ghost, and currently under house arrest in Switzerland charged with having sex with a 13-year old) "It's just about the work. It never came up. I was someone that he wanted to work with and I wanted to work with him. The feeling is that people in the business become really good friends and best buddies and it really is just a job," she laughs. "He's taken on a huge amount doing this film. He's also producing it, he co-wrote it and he has very specific ideas about what he wants. So, you know, there wasn't an awful lot of time to sit back and chat."
Cattrall's pragmatism is born of being on movie sets since she was a teenager. She was just 17 when she was picked out by Otto Preminger for a contract which was bought up a year later by Universal, making the actress one of the last signings to the studio's star-system. Her first film was Rosebud in 1975 – she took the role because the shoot was in France and she was broke. "I was far too young. It was horrific." Her big break wasn't all it was cracked up to be. "He [Preminger] was a horrible ogre. He thought enough of my talent to put me under contract and take a percentage of what I was going to make for the next seven years of my life," she laughs bitterly. "But that's a kind of double-edged sword. It didn't hurt but at the same time it wasn't the most nurturing, loving, wonderful introduction to the professional world of film."
She's learned her lesson since then. A childhood spent without much money in "freezing cold" houses across Canada ("we had a little heater we used to dress in front of...") followed by more than two decades as a jobbing actress, waitressing and babysitting between roles, moulded her into today's savvy operator. "I'm a good businessman. I pay my bills," she says. "Growing up in a situation where everything counted helps." When a Sex and the City movie was first slated, it was, apparently, Cattrall who held things up with her salary demands. "I felt that, at the end of the show, I wasn't set for life and other people were, and I felt that was not fair," she said at the time, referring to her co-star's Sarah Jessica Parker's reported $3m per episode. "The offer for the film just wasn't acceptable. I felt we should all make lots of money, not just one of us." It worked: Cattrall wound up with $6m, triple that of her co-stars, Cynthia Nixon and Kristin Davis (though still $9m less than SJP).
Today, dressed down in jeans and this season's biker boots, her face criss-crossed with lines, she is softer than her on-screen alter ego and more beautiful. This is her third run on the London stage, having appeared in The Cryptogram at the Donmar and as a bed-bound quadriplegic in Whose Life is it Anyway?, directed by Peter Hall. Both times she got glowing notices. "I'm not doing it to get great reviews. Although I would like it. I really want to do it to see if I can. There's something about living life in the question mark of 'am I capable?' Who knows?"
For now, the biggest challenge is mastering received pronunciation, which means her breathy voice keeps sliding, disconcertingly, from Noël Coward to Canada as we talk. Accent aside, she feels at home here, staying with an old friend rather than in a hotel, and proudly showing me her Oyster travelcard (though a car collects her tonight so it's not clear she actually uses it).
She is British Canadian, born in Wavertree in Liverpool before emigrating to Vancouver as a baby. She has family over here – including an aunt in Liverpool, who works in Marks and Spencer – and feels very British. "I don't express a lot of things that I feel, I kind of register things." Kim Cattrall has the famous British reserve? "A little bit. Compared to a lot of my American friends, yes, I see a difference."
Who Do You Think You Are? revealed the tale of her "sonofabitch" grandfather who abandoned his family (including Cattrall's mother) to a life of poverty in Toxteth, stowing away to America before coming back and starting a new family – without divorcing his first wife. Since the programme her mother and two aunts have made contact with their half-family and plan to visit them in Australia. Was she glad she did it? "I don't know, if I had known going in what it was going to be like, if I would have done it. It was quite an upheaval. I was angry for my mum. Rightfully so."
Cattrall, you surmise, has always been fairly self-sufficient. Having seen, aged 12, Janet Suzman's Rosalind in As You Like It at the RSC she set her heart on acting, leaving her family to train at Lamda before heading to Hollywood where she slogged away for years, building an endless list of credits including cult movies Porky's, Police Academy and Mannequin and every serial going – Charlie's Angels, Columbo, Quincy, Starsky and Hutch... It was Sex and the City, though, which changed her life – at the age of 42. "If it hadn't come along, I think I'd be alright too. I'd have a really good, strong, journeyman actress career. That would have been fine."
She wasn't convinced at first. Reading the pilot script, she saw only a "miserable" single woman, a group of people she "didn't care" about and a "depressing" picture of male-female relations. "When you sign a contract to do a series, you're effectively signing away six, possibly seven, years of your life based on 30 pages of dialogue. That's a little scary." Once she'd taken the plunge, she knew immediately that the chemistry was right, though it wasn't until the third series that the show really took off. Samantha's maturity, good heart and brazen exploits – in many episodes it was down to her to put the sex into the city – made her a favourite with fans and at the water-cooler.
She thinks the show has changed Hollywood's attitude to women. "Re-examining what happens to women in their 30s, 40s and 50s is, in some ways, incredibly new territory. I was driving to work and there was a big billboard with Denzel Washington looking like another film about the end of the world. Sex and the City really is something quite new and fresh compared to that. There's so much more to tell. It's also something that women crave."
She finished filming the sequel last month, with an eight-week shoot in Morocco. It was "massive amounts of fun and lots of giggles," and she'd happily do another one, as long as the story moved on. "It really depends on Michael Patrick King, whether he can envision another storyline for these women. If something doesn't grow, it dies. I can only say that I hope there's another one". You'd think she might be tired of, if not the character, then the reported on-set tensions. "You gotta laugh really. It's quite extraordinary. I don't think it's a good reason to stop doing something that you love just because there's some crap about it. Life is not neat and easy, it's complicated and silly sometimes." She and SJP text all the time – "You know, missing you, running, crazy, crazy oh me too baby. Blah blah blah..." – though she has yet to meet her co-star's "gorgeous" twins.
Ironically, for the show which claimed that women could have it all, Cattrall has sacrificed a marriage and a relationship to the show. "Oh my God, yes, absolutely," she sighs. "The most difficult thing about my job is that I do a lot of 19-hour days. It's really difficult to have a life, never mind a relationship. I don't have any regrets, really. I'm quite content. I'm very stubborn and persistent. I just keep working."
And if she eventually stops working? "I think I'd go to Italy actually. I have fantasies of it but then I think, God I'd be so bored. I feel like I'm living my fantasy in a way. I'm a very independent woman. I don't have to rely on anyone. I enjoy people. I'm very close to my family. I have pretty good values. I don't really want for much. It's all good."
Private Lives is at Theatre Royal, Bath to 20 February (01225 448844); Vaudeville Theatre, London from 24 February to 1 May (0844 412 4663). 'The Ghost' is released on 16 April