TWENTYSOMETHING

One Sunday afternoon at the end of last winter, a young woman went to a film - Sense and Sensibility, at the Curzon Mayfair in London. The girl was studenty-looking, in jeans and a jumper. She bought a single ticket, settled into her seat, and wept buckets. "I absolutely loved it. I thought, shit, this is so good." Nobody recognised her; nobody spotted that this was the girl on the poster outside, the girl who had stolen the reviews from the rest of a distinguished cast, the girl who had just won a Bafta, and was up for an Oscar.

Back then, audiences were unsure whether they were watching Kate Winslet in ringlets or Kate Ringlet in winslets. Six months later, she is established as Britain's leading young film star. Often these accolades are highly arguable, but in this case there are no other candidates. The only other Britons under 35 whom Hollywood will trust with a leading role are Ralph Fiennes, who is 33, and Julia Ormond, 31. Kate Winslet will be 21 on Saturday.

Like many a British actor before her, she has made her name in period pieces. Her last contemporary role of note was the girl in the Sugar Puffs ad. Her next role, at a cinema near you from next weekend, is another Penguin Classics heroine - Sue Bridehead in Thomas Hardy's Jude the Obscure, which has been renamed Jude (the notion of obscurity being anathema to the movies). After that, Winslet will be Ophelia in Kenneth Branagh's four-hour, 70mm Hamlet, which is now finished, but doesn't reach the screen till February.

So far, so British. But the escape route, the way out of the corset, already beckons. Emma Thompson (years into her career) made a contemporary American comedy with Schwarzenegger, and Helena Bonham Carter (years into hers) made one with Woody Allen. Kate Winslet, in no time at all, has gone closer to the tin heart of Hollywood: she is currently in Mexico, playing the female lead in an action movie directed by James Cameron, who made the Terminator films. Admittedly, this, too, is a period piece: it's about the sinking of the Titanic. But the point is, it's big; it's Hollywood; the part, an upper-class girl from Philadelphia, could have gone to Winona, or Alicia, or Liv. And it went to Kate.

The best thing about this meteor is that it is propelled by talent. Winslet is good-looking enough to have been named as one of the 50 Most Beautiful People in one of those fatuous lists, but she is far from your standard stunner: it would be truer to say that her face is capable of beauty. When I met her, in July, she was also giving interviews to two glossy magazines. Both talked of putting her on the cover; in the event, neither did. She just hasn't got that sort of look.

Talent, of course, is not enough on its own. Winslet's first role on the big screen, in the New Zealand film Heavenly Creatures (1994), was a gift: a character who was a teenager (heightened emotions), a play-actor (further heightening), and eventually a murderer (the ultimate high) - a scheming, screaming, nightmare of a person, and a dream of a part. Then she played Marianne Dashwood: a character who is not only a character, rounded and lovable, but a representative, an archetype, of sensibility. Sensibility! The very thing that actors have; the very thing that they are.

So when Winslet says, "I'm just so incredibly lucky," you think, you can say that again. And she does. A few minutes later: "I've been unbelievably lucky." Shortly after that: "I've been incredibly lucky."

Kate Winslet sits in a hired room at the Groucho Club in Soho. Her outfit is half girlish, half tomboy: a filmy black T-shirt under a black shift dress with a flowery pattern, rounded off with a pair of well-travelled Doc Marten boots. Her conversation is much the same: half luvvie, half earthy, with a clear echo of Emma Thompson, who played her big sister in Sense and Sensibility - off screen, by all accounts, as well as on. The message is clear: I may get all these period roles but I'm still a modern person.

Asked about Jude, which is set in 1895, she immediately makes a similar point. "You can well see it happening now, which I think is an important statement for period films to make - that actually times haven't changed, people haven't changed, emotions don't change, people are still having problems in and out of love. The only thing that's changed is the way we dress. Just because society and governments and whatever was different 100 years ago doesn't mean that people didn't have sex, pick their nose, swear..."

But the plot does hinge on society disapproving of a couple living together outside marriage.

"Well yeah," she says, with a trace of irritation. "But it wasn't uncommon then you know. The only thing I suppose that was so explosive about it was that Hardy wrote about it."

This is mirrored by Michael Winterbottom's film, a joint effort between his production company and the BBC. It's an uneven affair, with lapses into woodenness, but it has many strengths, not least the fact that it has been made at all. If there are moments of sunlit romance, the ending is far from a double wedding. There is one event so terrible that Hollywood would never have countenanced it, except maybe on Elm Street. But thanks to the present climate - the pulling power of Eng Lit, and Winslet - this unusual, unsparing, feel-bad film is opening at a broad range of screens across the country.

My guess is that the reviews for Jude will be better than the returns. But it marks another stage in the brilliant career of Kate Winslet. It's like what happens to young sportsmen, a couple of years in. You can get so far on natural talent, but there comes a time when you have to learn to use it. Winslet showed in her first two films that she has all the shots: a luminous presence, mobile features, a gift for mimicry, a large helping of charm, and an enhanced, almost volcanic sensitivity, which enables her to register emotions deftly, convincingly, and with a childlike intensity. In this third role, she adds the one thing the package previously lacked: restraint.

"In what sense?" Winslet asks, with another touch of frost.

Well, the performance is more held back, more suggestive (I say, trying not to flounder). But maybe that's the character.

"It's very much the character, but also I think -" she pauses, for the first time - "it's important not to do everything. It's so powerful in a scene where you just do nothing.

"That's something I've learnt, probably because Heavenly Creatures was so full on and I had to absolutely explode in every scene. Whereas Sue [in Jude] has a lot of stuff that she keeps to herself. And that's something I've really learnt about through working - my motto for a long time has been: 'Don't act, be.' "

When a director gives a big part to an actress with only one performance behind her, it is safe to assume that that performance impressed him. But the general admiration for Winslet's work in Heavenly Creatures was not shared by Ang Lee, director of Sense and Sensibility. "I am not convinced that was such a great performance," he told a reporter. "I saw a mad, horrific person."

When Winslet read for the part of Marianne - pretending not to know that her agent had put her up for the much smaller role of Lucy - Lee was captivated by her "bold, raw talent". Then he set about teaching her that less is more, spending more time with her than with any other actor. He was only partly successful: Marianne brims with passion, and Winslet hurled so much of herself into the role that she passed out twice. There is a memorable moment in Emma Thompson's diary of the shoot when Winslet has to be revived with a combination of flowers from the producer, four bottles of Newcastle Brown from the ADs (assistant directors), and the chance to warm her sodden feet by placing them in the armpits of Greg Wise, whose character, Mr Willoughby, was the cause of all the trouble.

No such stories have seeped out of the shoot for Jude, or Hamlet. But in person, Winslet does her best to keep up appearances. One of her eyes, which are normally an interesting blue-green, is black, with a nasty bruise just on the edge of the iris. "I was violently sick the other day," she explains. "So violently that I burst a blood vessel.

Acting is in Winslet's blood, but success is not. Her father is a struggling actor, and so is her elder sister, who still lives in the family semi in Reading. "I come from a background of actors who have never worked hardly ever and always been right on the breadline ... my sister has a terrible time and hardly ever works, and when she does work they're always kind of small theatre jobs with little touring companies up North that go from school hall to school hall."

It must be tricky.

"Yes, absolutely. It's heartbreaking. It's not that - there's never been any jealousy on their part. I just wish I could do something for them, but obviously I can't. I mean there are certain conversations I can have - 'Oh look will you see my sister for this or perhaps you'd consider Dad for that?' and hopefully Dad will get something on Titanic because he's met Jim Cameron and Jim thinks he's fabulous.

"It is difficult but what I love about my family so much is that they never, ever have looked on anything that I've done as glamorous. And as soon as it has got to that level, I immediately invite them into it to experience it with me. Sometimes when you do the publicity thing over in the States, you're treated like a queen. And it's important to me that my parents really see that, and that's why it was so good having them both at the Oscars."

She took them with her?

"Yeah, they both came and they were like kids, they couldn't believe the fun it was. I'd say to them, 'Go on, just go for it, someone else is paying, you might as well have a laugh,' and we really did have a laugh. It was like one of those supermarket sweep things when you can just go around the shop and grab anything you want."

Her "constant ambition" is to be able to erase her parents' financial worries. "Until I buy them a house, I won't feel I've cracked it."

Titanic, in which she stars opposite Leonardo DiCaprio, will pay more than her four previous films put together. The money has brought her a personal assistant ("It's ridiculous - I'm only 20 and I've got a PA") to go with the personal trainer supplied by the studio. It won't buy a house for her family, but it has provided a flat for herself - "a huge place, first and second floor, in north London", which she had moved into the week before we met.

She waxes lyrical about the joys of nesting, of linen from John Lewis and a bed of her own, kingsize, from "this brilliant place called the Big Table". If this sounds gushy, her choice of flatmates shows that the Doc Martens are still somewhere near the ground. She is sharing not with a man, or a fellow actress, but with two backroom girls - a make-up artist and an assistant director. A star who makes lasting friends among the crew is a star with sense and some humility.

Does she worry that the bubble will burst?

The torrent slows; her tone softens. "Um - I mean - I don't know that I do worry. Maybe there will come a point that I will need to worry about it, but - I do worry that what could happen is that old thing that happened to Winona Ryder. She worked worked worked and then stopped, because people just got bored. But to me it's not some sort of career ladder, it's all about the work, and as long as I carry that mentality with me I should be OK."

I rang Kenneth Branagh's publicist, and asked for a comment from Branagh, to get an actor-director's view of her abilities. When the quote came back, it was more about her personality: "When I first met Kate, I thought she was 29. After the meeting the casting director told me she was 17. She has a very old head on young shoulders, which is currently keeping her sane in the midst of extraordinary success. My first and lasting impression was of having met a real 'natural', a genuine star. I think she'll cope."

One of Winslet's lesser coups is to have got on well with Emma Thompson and now with Branagh. She speaks warmly of him, in the usual way ("incredible ... amazing ... life-enhancing"), but also makes a more precise point: "There's nothing canny or clever about Ken. He doesn't play director games, he never makes you feel stupid." This sounded like an oblique reference to Ang Lee, who made his cast write essays on their characters, marked them, and famously said to Winslet after her first day's work, "You'll get better".

Winslet didn't have to write an essay on Ophelia, which is a shame, because her take on the character is inimitably Winslettian:

"I hope I've made her strong, I really hope so. If you think about Ophelia, she's this girl who's never had a strong female presence in her life. And she's in that funny transition period, going from her teenage years into really becoming a woman. She's having this pretty full-on relationship with Hamlet, but she always seems to be suffering. She's the victim of everything, of everybody, this little floaty thing that's just sort of dancing about. She's never a solid character. I thought, sod it, she should be. She's hung on to herself and been incredibly strong through this life which at times I'm sure has been terribly lonely. There's her brother who she loves and he's buggered off to France to have a lovely life thank you very much, and her father Polonius - you know, stuffy old git who's trying to keep her wrapped up in cotton wool - has just been promoted to Prime Minister. And with her lover Hamlet she's going through this awful time because he doesn't know what the hell's going on, and she's having to deal with that. And if she suffers, it just seems daft and you know that she's going to go mad from the minute you see her. So I thought no way, that's been done before, people are going to get bored. So I just tried to reverse the situation and give her a purpose.

Brodie's Notes were never like this.

! 'Jude' (15) opens nationwide on Friday.