Kate Winslet is back in a corset for her latest movie, Finding Neverland, the story of Peter Pan author J.M. Barrie's relationship with a young widow whose children provide the inspiration for his famous characters. But it's just another day at the office for the down-to-earth star who refuses to let marriage to a famous movie director and a place on Hollywood's A-list change her. The girl next door talks to Donald Clarke

'Could you do me a favour?" Kate Winslet asks me. Lie in front of a train? Ram my arm into a threshing machine? Watch two Ben Affleck films back-to-back? Anything.

It transpires that Kate has become involved with a competition named Bounty Hunter on some radio station or other. As I understand it, members of the public arrange for a celebrity acquaintance to phone the relevant show. A poll is then carried out to determine which entrant has delivered the most impressive famous person. The winner receives £10,000 with £1,000 being awarded to a charity of the celebrity's choice. As we speak it is a three-way-tie between Kate, the guy who played Zammo on Grange Hill and Angleina Jolie.

"But it was Angelina's personal pilot who phoned in," she explains.

Well, he can't need the money.

"That's what I thought. But my friend is about to get fired, so she really needs the ten grand." I hand her a pen.

"OK. So this is the website and you have to tell all your friends to vote for Kate Winslet." She writes her name clearly on the card before, with surreally unnecessary precision, adding: "That's me. Kate Winslet." I'm so glad she has turned out to be a good egg. We have got used to the fact that Bing Crosby wasn't such a lovely old buffer and that Arnold Schwarzenegger isn't a robot from the future, but it really would be too much if Kate Winslet, with her upside-down smile and her slightly clumsy physical manner, turned out to be a self-absorbed toad.

Winslet's more easily upset fans should, despite its being a very enjoyable middle-brow entertainment, approach her new film, Finding Neverland, with a modicum of caution. Telling the story of the relationship between J.M. Barrie (Johnny Depp), the author of Peter Pan, and the young widow whose children became the inspiration for the Lost Boys, the picture begins amiably enough, then, about half-way through, Winslet begins coughing into a hankie. When people cough in the movies, they never have a cold.

"Did you cry?' she asks.

Like Paul Gascoigne. Like Tiny Tears. Like Johnny Ray. People were pointing and laughing.

Kate punches the air and makes a "woo hoo" noise.

"That's what we want: more grown men crying. I think it is good for a man to have a cry now and then. Excellent!"

You can see why Winslet is so popular with the lads (interestingly, women's magazines have often been a bit snitty about her). She gives the impression of being rather good fun in a way that, say, Nicole Kidman does not. I bet she likes a game of Subbuteo now and then. I can imagine her betting her husband, the director Sam Mendes, that she can spit farther or hold her breath longer. I suspect Juliette Binoche never says "woo hoo" in interviews.

She is, of course, also rather easy on the eye. Dressed today in a black halter-necked top and blue jeans, blonder than she has sometimes been, she looks. . . Well there is nothing more nauseating than an interviewer going on about how ravishing some movie star is, so I won't. Not that Winslet would describe herself as a movie star. Indeed, when I say those words she visibly winces. Come along, she is in the Dorchester Hotel promoting a film starring Johnny Depp. Get real!

"This is where I get so embarrassed," she says. "A movie star? I just don't feel I belong here at all. I find myself in the Dorchester, some posh hotel I never thought I would be in. I still find it all so exciting."

Kate was born to theatrical parents in Reading in 1975. She acted throughout her teens, but, aside from a brief appearance alongside the Honey Monster, never made much noise as a juvenile. Her big break came in 1994 when she was cast in Peter Jackson's Heavenly Creatures, the true story of a notorious murder in 1950's New Zealand. Then came Ang Lee's Sense and Sensibility, Kenneth Branagh's Hamlet and some film about a boat.

"I was completely at a point after Titanic where doing things like this - coming to the Dorchester - was becoming a bit of a drag and I didn't even look at the wallpaper or what lovely drinks I could order or how comfortable the seats were. It was just like walking through an airport terminal and not looking right or left. During filming, people were saying: 'How will this change you?' And I was adamant that it wouldn't change me. But the truth is it was hard to live a normal life in my little flat in London N7 after that. I was being door-stepped. My car was chased. It was horrible."

I wonder if her decision to follow up Titanic with smaller, more eccentric pictures such as Jane Campion's Holy Smoke and Gillies MacKinnon's Hideous Kinky was part of a conscious attempt to get back to basics.

"Oh definitely," she says. "Very much so. That was about survival. Not to mention that I really liked those scripts and often the big-budget films these days don't have such great scripts."

What was the dumbest thing she was offered? "Oh something with robots, I think. I am not really the action movie type. I was running around a lot in Titanic. But my wobbly bottom was corseted in."

It is easy now to forget that during the production of Titanic movie pundits, often using the real ship's demise as a clumsy analogy, consistently suggested that the film might prove to be the biggest flop in Hollywood history. The production was way over budget. Chaos reigned on the Mexican set. And Kate spent much of the shoot waist deep in icy cold water.

"It was part of the job. It just didn't occur to me that it was odd," she says. "It wasn't like we were being mistreated; that was just part of the job and we happened to be shooting in ice cold water that day. But we British actors are relatively uncomplaining. What you see is what you get with me. I am the same on set as I am right now, I hope. As far as all the press speculation went, we didn't really hear much of it."

In the aftermath of Titanic's success, a recurring strain in press coverage of Winslet made its first appearance: musings on her weight. Honestly, to read some of the coverage at the time you'd think she was the size of Hattie Jacques and that comical tuba music greeted her entrance into any room. Firstly, she was portrayed as a proud defender of a woman's right to be curvy. Then she was, apparently, a little too fat. Then she was a traitor for giving in to the system and losing weight.

"I am afraid that still goes on a bit," she says. "My agent will get phone calls from cosmetics companies and the first thing they say sometimes is 'How is her weight currently?' And my agent will just say thankyou and put the phone down. And what is so annoying is that I don't have a weight problem now. I was a chubby teen and after Titanic my weight went up and down for a year and then I had a child. When they called me Weighty Katy it did hurt, because there were times as a teenager when I was eating less than was healthy. I had to be careful that didn't happen to me again.

"But at least it was just that from the press and not me being photographed in the gutter after the latest orgy of cocaine. I have, thank goodness, never been that sort of person."

And then there was the bizarre incident last year where photographs accompanying an interview in GQ magazine were touched up and morphed to the extent that she ended up looking like an eight-stone giant.

"Oh that thing was really pointless," she sighs. "I think they just did it to create a kind of controversy. But there was an assumption that I would be happy about it; that's what drove me the craziest. I was very unhappy about it. All magazines tend to do retouching to get rid of moles and so forth. But the people that buy the magazines don't necessarily know they are retouched and therefore a lot of women will look at them and say: that's how I want to look."

In 1998 she married James Threapleton, who had been an assistant director on Hideous Kinky, and in 2000 they had a daughter, Mia. Initially, the press was back on her side: how refreshing that she was dating "below the line" (industry speak for the less starry members of the cast and crew); wasn't it great that they had bangers and mash at the reception? Then things turned ugly when the marriage broke up.

Rumours abounded that the relationship fell apart because one partner was a little too famous for comfort. It was further suggested that she had begun dating Mendes, the director of American Beauty and The Road to Perdition, while still with Threapleton.

"On the whole, I don't talk about that," she says. "All I can say is that stuff was all rubbish. That stuff was a bitter pill to swallow, but divorce itself is a difficult pill to swallow." Things seem to have worked out OK. In June 2003, she and Mendes were married in the West Indies and later that year she had a son, Joe. So tell us all about how terrific Mr. Mendes is.

"Oh, well, look. I just really don't talk too much about my private life." She suddenly looks enormously uneasy. Curling up on the sofa she focuses acutely on the floor and begins twisting one hand about another.

"Well, er, um. It is just great. What can I say? I am very lucky, very happy. We have the two most wonderful children. He is such a brilliant dad and a great step-dad. We are really happy. What else to say?" Rescuing her from obvious discomfort, I ask her to tell us about her extraordinary ability to injure herself on set. She has just finished shooting John Turturro's bizarre sounding musical, Romance and Cigarettes, with James Gandolfini, Susan Sarandon, Christopher Walken, Eddie Izzard and everybody else. Somehow she managed to do something ghastly to her ankle.

"Oh God, that was awful. I was dancing in four-inch heels and just tore all the ligaments in my leg," she says. "But something always happens to me. I was battered by fake rain in Sense and Sensibility and fainted from the cold. I have scars everywhere. I have scars on my knees from falling on the deck on Titanic. Here look at this." She leans forward and rolls back her sleeve to reveal a pale, thin line on her wrist.

"That was from Holy Smoke. It was this scene where my sari was being pulled and it was pulled over my wrist and burnt me." I suddenly feel as if I am in the scene from Jaws where Robert Shaw and Richard Dreyfus compare wounds. I suppose it would be highly inappropriate if I showed her one of my scars.

"Oh don't worry darling. I've seen it all."

Like I said, she really does come across as one of the lads. The listeners to X-FM seem to agree and, holding off a late surge from Dame Judi Dench, her co-star in Richard Eyre's Iris, she triumphed in Bounty Hunter. Zammo held on to the third spot. Angelina was nowhere.

Finding Neverland opens on October 29.