Olivia Williams: Growing up in public

The actress Olivia Williams was best known, until recently, for being jilted by Jonathan Cake and 'discovered' by Kevin Costner. She tells Laura Tennant why she feels like her own woman now

Olivia Williams is the kind of actress who was born to stalk tragically through a grand London house in full-length bias-cut satin with only a gash of red lipstick to indicate the turmoil within. So it's no surprise that the director Thaddeus O'Sullivan wanted to cast her in The Heart of Me, a tale of two sisters, the man they share and the children they lose, set over the war years. Based on Rosamond Lehmann's The Echoing Grove, it features excellent and affecting performances from Williams and her co-stars Paul Bettany and Helena Bonham Carter. But when Williams was sent the script, her first thought was: "Once again I've been sent the role of the cucumber-up-the-arse sister and I want to play the crazy bohemian one. Why am I always cast as someone who can't show what they feel?"

It's true that playing posh and repressed has been something of a feature of Williams's career, but, as she acknowledges, the most interesting characters are people "who are not letting their emotions hang out, who are trying to suppress them, because that is what most of us do most of the time". In person she is appealingly frank and fearless, happy to be that most unfashionable of things, serious-minded, and unapologetic about her elite education and upper-middle-class background.

Nobody likes to be misquoted, but one senses that for Williams it is a particular torture. "As you know, I studied English and I try to choose my words very carefully and put them in an order that I've thought about. My vocabulary has been worked on and I strive to broaden it and make it interesting. So when I talk to journalists," she continues with an ironic twinkle, "I sometimes long to say, 'Why don't you let me e-mail you that anecdote?', so that I know they'll get it right."

We meet in the actor's café at the National Theatre, where she is playing the Princess of France in Love's Labour's Lost, Sir Trevor Nunn's farewell production there. On stage Williams manages to be both playful and superbly queenly, and she and the production, which moved me to tears, are enthusiastically applauded. Theatre, she says, is her passion, even if rejection and bad reviews are that much more bruising "when you are personally present at your humiliation. Film acting is a job I love, but it's like being kidnapped by aliens, and everything that happens is extraordinary and fun, even if the result is dire. And with film there are so many things I've chosen not to buy into – the Hollywood diet, for instance – that if they don't choose me I can blame not being famous enough, or whatever. With the theatre," she says, affecting a tragi-comic manner, "it's just me they don't want."

In fact, Love's Labour's Lost was her first stage appearance for eight years. She has worked steadily in film ever since Kevin Costner cast her in The Postman in 1997 (of which more later). This summer The Heart of Me will be joined by To Kill a King, Mike Barker's drama about Oliver Cromwell and Thomas Fairfax, in which Williams plays Lady Anne Fairfax. At Christmas we have PJ Hogan's Peter Pan to look forward to; she plays Mrs Darling.

"The fact that I have been able to earn money as an actor is largely down to luck," she says, with genuine modesty. "I was very close to giving up when Kevin Costner made his infamous phone call." She was 29, and it was her big break. "I got home to several thousand messages from my agent's assistant saying Kevin wanted to speak to me, when would I be in? I invented a pressing engagement that would keep him waiting a little longer while I paced around the flat practising how I would say 'Hello.' He called, said he liked my audition tape and would I do another. For some bloodyminded reason I refused, and the conversation ended cordially, but rather awkwardly. The next day my agent rang telling me I was to fly out the following day."

Costner cast her as a plucky American frontierswoman, and although the film flopped, Williams didn't. The critically well-received Rushmore with Bill Murray followed, and then The Sixth Sense, in which, lucky girl, she played Mrs Bruce Willis. But though we British quite like sending our young actresses "over the top" in Hollywood, Williams was not so silly as to be chewed up and spat out by that giant maw.

"I love the place to go and visit and I love working there, but I haven't got the stamina to maintain myself at the level required to be a regular attendee at award ceremonies and premieres. I go to a couple a year, and have a great time and do all the waxing and polishing and dying that is required, but on a day-to-day basis I can't face it. And also I don't want to put all my eggs in the appearance basket because it's too distressing when it screws up. It's too awful when a bad photo comes out of you and it ruins your employment prospects. It's cowardice on my part in a way."

Costner famously described her as "one of the most beautiful women to come on screen in the last 10 years," but, says Williams, "I like to think I'm coldly professional about my appearance. Kevin actually didn't recognise me from my audition video; what he said was, 'Something extraordinary happens to your face in two dimensions.' I'm lucky; shot in the right light, from the right angle, I'm very photogenic."

(And reader, it's true; stand her in front of the poster of herself outside the theatre, and most people would walk straight past her, as she will cheerfully admit.) Fortunate, and very unusual, is the thirtysomething female who cares not a jot about her first wrinkle; how much more fortunate the actress who can view it with equanimity. "I work very hard to banish the fear of getting old," says Williams. "My father was very ill a couple of years ago and his body gave out on him for a while. When they wheeled him out of heart surgery I thought, my body works. My skin may have wrinkles but it's because I'm smiling so much. That might sound like some terrible American greetings card, but I feel it's immoral for me to castigate my body for getting older, when it does everything I ask of it."

Williams's rather severe and classical beauty is suited to maturity. "I didn't get to explore ingenue," she says, "because as someone once said, I was always too genue." Even as a teenager at South Hampstead High School for Girls (Helena Bonham Carter was in the year above) she was precociously advanced, preferring the company of her parents to that of school friends, listening "to a lot of Bach cello suites" and reading "a lot of Gerard Manley Hopkins". She was passionate about ballet, and had toyed with the idea of the Royal Ballet School, but decided, at the age of 11, that the academic standard wasn't high enough. By 16 she was too tall and "slightly too broad in the beam" for dance and intended to follow her much-loved and admired parents' footsteps into the Bar. In fact it wasn't until she left university (she was at Cambridge) that she decided to take acting seriously, an irony that is not lost on her. "I got a place at the Bristol Old Vic Theatre School to study acting for two years because I loved it, but I still didn't regard it as a career choice. The Old Vic was all vocal exercises and being told you were shit, which wasn't quite what I had in mind, but I also learnt that to half do it was offensive to those people whose dream was coming true by being there. So I sorted my ideas out and worked at my 'craft' – and that's in inverted commas and intended ironically, by the way..."

It was at Cambridge that she met Jonathan Cake, the long-term boyfriend who, after a lot of shillyshallying, finally proposed seven years into their relationship, only to change his mind two weeks before their wedding day. Cake was then starring as Oswald Mosley in a TV dramatisation of his life, and the story was widely reported.

Shortly afterwards Williams got the call from Costner and since then her star has eclipsed Cake's. Does this circumstance give her quiet satisfaction? "No," she writes to me after our interview in a characteristically precise e-mail. "I feel much more smug that my theory that hard work and talent and wanting something so much and believing in yourself and following your dream in the execrable thespian tradition, bears absolutely no relation to one's eventual success or failure in this business. There is no justice in the difference in our fates."

So how is the audit looking, personally and professionally? "A year ago it wasn't good," she says wryly. "Despite all the wonderful things I'd done, I thought, this isn't where I want to be now; I was still living in the same flat and I was as emotionally frustrated as I was when I was 22. All my friends with children hated me because someone could ring up and say, 'We need you to go to Australia for three months next week' and I could go, and how lovely is that; but also how depressing is that, that no one says, 'You can't leave, I need you here.' That's how you get to 34 and think, Jesus, I'm still dating like a teenager and I don't have any kids."

Since then, there have been developments. She's moved into a new flat, in Marylebone, and has a new boyfriend, the actor Rashan Stone ("He's lovely and we're very happy"), who has just finished a sell-out run of Simply Heavenly at the Young Vic. She's serious enough about him not to want to be parted from him for too long. Holding out for her full fee probably cost her a role as the new Bond girl in Die Another Day (the part went to Rosamund Pike), but on balance she doesn't regret losing that particular gamble. "It would have meant five or six months of flying back and forth to Iceland and America and not being able to take any other work. That kind of commitment would have to buy you a house in Tuscany, and you still might end up paying for it with your relationship."

In the National Theatre café, the cast of Love's Labour's Lost are being called for a vocal warm-up. There's time for a final question before she strides off to prepare for the performance. What does acting do for her? What need does it supply in her? "After first days of filming sometimes my driver will take me home and say, 'What kind of crazy drug are you on?' And I'll say, 'I'm just really happy because I've been acting all day.' But in the theatre there's even more of a post-performance high. If someone meets me for a drink after the show, I'm insufferable, like a dizzy teenager. Between curtain up and curtain down I'm incredibly happy."

'The Heart of Me' is released on 2 May