If you've ever wondered whether movie stars enjoy shooting sex scenes, think of Diane Lane, star of Unfaithful, whose wild clandestine romps with co-star Olivier Martinez take place in a bed, on a landing and up against the loo wall in a New York cafe.
'Difficult? Oh my God, yes,' she says, nodding seriously. 'You see, Adrian's a yeller.'
Adrian Lyne, the acclaimed British director, is an old master at making celluloid sizzle, having already directed 9? Weeks and Fatal Attraction. His on-set technique, however, involves cheering the stars along like a coach from the sidelines.
'Stuff like, "That's it! Great! Go! Go! Do it again!"' says Lane, laughing. 'I had to ask him to stop. His other trick was to shoot a whole magazine of film, so one take was as long as five takes. By the end, you're physically and emotionally shattered' She sips her water and picks lint off her crimson tonic jacket. 'It took a lot out of me - it was like having a baby. I haven't worked since. Still recovering.'
We're sitting in a sterile suite at the Four Seasons Hotel in Beverly Hills for one of those allotted half-hours on the 'international press' carousel. It's the kind of drive-through interview that tends to give an actress the distant cordiality of a flight stewardess, smiling but with the defences firmly in place. Not Lane, though. She's warm and frank and happy to talk sex scenes from the off. 'It's all part of the job,' she laughs. 'And believe me, talking about it is easier than doing it!'
That Lane is working at all counters a theory or two about child stars. After all, there was a time when she was so set for success that failure seemed inevitable. Her first film, A Little Romance, propelled her to the cover of Time at the age of 14. Her co-star Laurence Olivier hailed her as 'the new Grace Kelly' and Francis Ford Coppola cited her as his favourite young actress. She was worth millions by the age of 18 and had the world at her feet, but instead of soaring to Jolie or Paltrow heights, or indeed careening into a muddle of drug abuse and therapy, Lane spent the 90s as a 'working actress', a hidden diamond in a string of also-rans and occasionally excellent indies.
After years below the celebrity radar, she has lately emerged as a seasoned talent in need of a worthy script. Her turn as the evil-junkie stepmom in The Glass House was suitably debauched, and she was every inch Mark Wahlberg's brave and sobbing widow in The Perfect Storm, her 41st credit.
Yet all of this pales into the past now that Unfaithful is out. It may well return her to the fame she has successfully ducked for so long. Lyne is used to hits, and infidelity is his major theme - he followed Fatal Attraction with Indecent Proposal - so Unfaithful should be a decent bet at the box office. 'Lucky number 42, I call it,' says Lane.
Loosely based on La Femme Infidèle, a 1969 film by Claude Chabrol, Unfaithful tells the story of a suburban wife and mother who falls for the Gallic charm of a handsome young Frenchman (Martinez) in Manhattan. (Lane herself married a Frenchman - the actor Christopher Lambert, with whom she had Eleanor, now eight - but she denies this made the scenes any easier. 'Anyway, my marriage ended in divorce.')
As Martinez becomes a mounting obsession - in every sense - their liaisons become increasingly urgent and unbridled until eventually her foursquare executive husband (Richard Gere) uncovers her betrayal.
Cue murder, guilt, cops, tears and a wrenching moral aftermath that ends, radically, in ambiguity - the good kind, the kind that makes you wonder what will or should happen next.
The final frame was fought over to the last. Initially, 20th Century Fox was uncomfortable with the enigmatic ending since it left crimes unpunished - a no-no in Hollywood. So the studio imposed a diktat, a particularly jarring 'Hollywood' final line.
'Oh, but Richard was furious!' says Lane. 'Furious! "Who put this in there?" - he was pointing at these cowering executives. And they were pointing at each other. "It was him!"' Ultimately, Gere's wrath and the reaction of test audiences forced Fox to concede, barely a fortnight before the US release, to running with the film's original, haunting conclusion.
Unfaithful's strength is its acute observation of what Lyne calls 'the body language of betrayal'. The parts are so nuanced and the script so lean that what might have been a standard morality tale becomes instead a complex, sympathetic portrayal of all three players - the cheat, the cheated on and the catalyst. You feel for Gere and almost forgive his crime, Martinez is disarming and unpredatory, but most improbably, your heart goes out to Lane. Since her guilt is so transparent, a tribute to her performance, she remains ultimately moral. Lane has created, not for the first time, that most un-Hollywood of characters: the mature sympathetic adulteress.
Though she would never excuse her character's affair, Lane explains the impulse to cheat as a need for excitement. 'There's a certain amount of drama that people require to feel alive,' says Lane. 'Some people need really large weddings, others have road rage, some actually cut themselves... Best, I think, to know that part of yourself. Because it will surface.' Thankfully, Lane's own appetite for drama is sated by work. 'Acting,' she says, 'is how I freak out.'
To Lane, the job of acting could not be more ordinary. The only child of acting coach Burt Lane and Playboy centrefold Colleen Farrington (Miss October 1957), she grew up in bohemian New York around such family friends as John Cassavetes and Gena Rowlands. Her stage career began at six, as a full member of La Mama, a globe-trotting avant-garde theatre company. 'Every summer vacation I went off with them - just me, without my parents - and we travelled to Scotland, Finland, England, Italy, France, all over Europe.
I made $50 a week.' Lane recalls playing Medea, in the original ancient Greek. 'The lines are seared into my head to this day,' she grins.
She was 13 when George Roy Hill, the director of Butch Cassidy and the Sundance Kid, cast her in A Little Romance in 1979, which led to the Time cover. 'Even then I understood that it wasn't about me and that this was just the publicity machine of the studio at work,' she says. 'I saw Henry Kissinger in the corner of the same cover and the mythology of celebrity just fell away.'
By the age of 19, however, with 14 movies to her credit, Diane herself called time on her inimitable ascent. As Matt Dillon's girlfriend Patty in Coppola's cult classic Rumble Fish, she had conquered the teenage-siren role and was casting around for a lead to catapult her into the firmament once and for all. But she turned down Splash, which was a hit for Daryl Hannah, and opted instead for Streets of Fire and Coppola's next film, The Cotton Club, which both turned out to be high-profile flops. Why? Lane still doesn't understand, particularly in the latter's case. The Cotton Club, in 1984, was the last time she acted alongside Richard Gere, who was twice her age (she was 18). 'It was a good film, but it just became this punchbag for the media,' she muses. 'Why is it when you get lots of chimps together, they maul one of them to death? Is it a culling process?'
She escaped to Georgia to discover 'where I began and my career ended', which took two years. And on her return to the business, she picked parts with mixed success - 'lessons were learnt, agents were fired' - but she has worked steadily for 15 years and emerged a model of confidence, self-respect and sanity. (Which does for the remaining theories about child stars.) 'You can't get work without working,' she explains, breezily, 'and if they knew what made hits they would make more of them! It's a crapshoot. That's my bumper sticker about the whole thing.'
In acting terms Lane is wise beyond her 36 years (another Lane bumper sticker: 'It's not the model, it's the mileage'), but she has none of the typical anxieties that accompany the advance in age. In fact, she's so refreshingly comfortable in her skin that when asked what she would change about her looks if she could, she doesn't umm and ahh about 'my nose' or anything so cosmetic. 'I wish I could always look like I've just finished a really good laugh,' she says.
She is also defiantly anti-fabulous, at best bemused by the celebrity circus of which she was once a part. As almost an affront to the mythmakers of Hollywood, for example, she deliberately missed the Oscars this year. 'I had gowns hanging, jewellery ready, and I just opted out,' she says, beaming. 'It's an attitude I enjoy thoroughly. I didn't feel like "putting it on", so I wore my house slippers and went to my girlfriend's house. You know, I've done very well without celebrity for a very long time and I think I'm a different animal for it.'
If she doesn't want Oscar tickets, doesn't she want a man in her life? She dated Jon Bon Jovi and Matt Dillon during the 80s, and was married to Lambert until 1996 - a man that she has described as 'the complete opposite of someone who could give me what I needed'. But since then she has remained resolutely single.
'I don't want a relationship. It's far too complex with a child,' she says. 'There's an innocence there and an image of myself in her eyes to protect, so I'm not going to fumble around in my own emotional life. Besides, relationships don't fit in with your life. You're consumed by them and your priorities change.' For the time being, then, Lane's life happily revolves around her only child, Eleanor.
The cliché goes that parents wish for their children what they themselves never had. It is no different for Lane, who is obsessed that her daughter not be railroaded into showbusiness and premature stardom as she was. 'When I was 12, all I wanted was to be good at school,' she says, 'and to do something admirable, something you can't take away from me because I'm not popular or beautiful enough.'
And you can't help but think that Diane Lane is now as popular and beautiful as ever, and that little Eleanor could do a lot worse in terms of role models.
· Unfaithful is released on 7 June.