Abbie Cornish

Women knew their place in polite society in early 19th century England, or were supposed to. They didn't speak out of turn. They were always chaperoned. They waited passively while their lives were shaped by others.

The secret love affair between the doomed, tubercular poet John Keats and his beautiful, half-educated, 18-year-old neighbour, Fanny Brawne, takes place within this restrictive ambience in writer-director Jane Campion's subtly erotic Bright Star. The challenge is to convey intense passion without being able to show anything more intimate than a hurried kiss. Campion achieves this through her inspired casting of Ben Whishaw with Abbie Cornish, allowing their obvious empathy for each other to bring alive the relationship they portray.

"Abbie is completely direct and real, but there's a kind of looseness, freedom and vivacity to her which suits the character," says producer Jan Chapman, who previously worked with the Australian actress on her 2004 breakthrough film, Somersault. "She has an incredibly direct gaze but can also express youthful, uncontrolled feelings very well."

When Cornish, 27, first met Whishaw, she shook his hand and said, "G'day, mate." She laughs as she recalls the moment.

"It didn't take much time or effort at all to get to know him," she tells me. "I kind of instantly fell in love with the guy. He's gorgeous. He's so sensitive and open and honest. It's very easy to be who you are with him and to be intimate with him. We liked each other from the start, and then over time developed this space where the both of us could be who we are and act what we had to act without any feeling of reserve."

It had been much the same with Heath Ledger, who played her junkie lover in Neil Armfield's Candy three years ago. "I love her," he said. "She's like my little sister."

They went to Narcotics Users Association meetings together and even shot a mini-documentary to show to the Candy crew.

"It was much more practical," says Cornish, "much more tactile, much more talking and getting in cars, talking to heroin addicts and their families and experiencing what it feels like on the street at night. We had to learn about what heroin does to someone and how people use heroin. Bright Star was just reading poems and textbooks and letters and looking to history. There are always things you can relate to in a character and things that seem really foreign. It's you and it's not you."

She had no thought of becoming an actor, growing up on a farm in Lochinvar in the Hunter Valley of New South Wales.

"I was more interested in being a vet or a musician or a painter. Acting wasn't on the cards until I was 15. I'd help Dad round up the cows and stable the horses. It was the biggest playground you can imagine. It really helps your mind grow. You learn to invent and fix things. You never feel restricted in what you can do or where you can play."

She experienced much the same sense of freedom living in the south of France playing Russell Crowe's fresh-faced young American cousin in Ridley Scott's romantic comedy A Good Year. She'd been there before as a teenage backpacker after her parents' divorce when she was 16. While still at a Catholic school in Maitland, she won a Young Actor's Award for her role in the TV police drama Wildside. Then Cate Southland cast her as the runaway in Somersault.

"There are differences when you're directed by a male or a female director, particularly for me," she says. "Men and women are different. Both [Cate and Jane] have the kind of woman nurturing thing. It's the mother in us or something. Sometimes I'd do a scene in Bright Star and I'd look up at Jane and she's crying. I haven't seen a male director do that."

She doesn't see Bright Star as a period film. "Jane told us at our first rehearsal not to feel we were stuck in 1820 but see it as a timeless love story that transcends its day and age. It's like Keats' poetry. You don't feel when you read it that it's unreachable, that you can't understand it. It feels very real."

She breaks off to murmur lines from a poem he wrote to Fanny: 'Pillowed upon my fair love's ripening breast/Feel forever its swell and fall.'

"So I didn't try to analyse their love. Ben was just totally Keats and I was totally Fanny, so you just go with that. We didn't know when we were going to hold hands or kiss. Nothing was choreographed. We knew Jane would just choose the moments that she loved the most. There was a kind of freedom in just being the characters and at a certain point it's… and now they kiss."

She'll next be seen in Zach Snyder's Sucker Punch, playing a girl in a psychiatric ward in the 1950s who is trying to escape with four other girls. It's as far as she can get from Bright Star or The Golden Age, Shekhar Kapur's follow-up to Elizabeth in which she played a lady-in-waiting who became part of a love triangle involving Cate Blanchett's queen and Clive Owen's Sir Walter Raleigh.

When Bright Star premiered at Cannes, she was with Ryan Philippe. They met last year filming Kimberley Pierce's Stop-Loss, a Gulf War drama about soldiers who return from Iraq and try to readjust to civilian life. So is she romantic?

"Yeah, I think so." Does she believe in the 19th century Romantic idea of love being forever? "I don't know, really. You don't know what's going to happen next in life."

'Bright Star' opens on 6 November