Kate Winslet and I are standing side by side on what feels like the edge of the world. It is a cold, clear day and on this vast expanse of beach on the English south coast, sand and sea have merged, glittering, into one. "Isn't it just glorious?" she sighs, holding her blond hair, which is being whipped by the wind, away from her face.
In profile there is something about this face that is hard to look away from; a powerful beauty that feels strangely familiar. This, of course, is because it is a face we have been watching on screen for 20 years. Since starring in the film Heavenly Creatures at the age of 17, Winslet has forged an almost faultless reputation as one of our greatest living actresses.
In most cases this might be hyperbole but in Winslet's it is true. Who but she could find the humanity in a spoilt heiress (Titanic) and a Nazi war criminal (The Reader); be as believable as a free-spirited English author (Iris) as a repressed suburban American housewife (Revolutionary Road); and command a television audience's attention for five whole hours as a single mother trying to forge a career (Mildred Pierce)?
In person, as on screen, Winslet, 38, defies you not to be drawn to her. Warm, unguarded and funny, with a filthy mouth and a guttural laugh, she gives a pitch-perfect performance as the consummate interviewee. She even comes armed with refreshments, a Thermos bag full of three types of tea and delicious homemade biscuits.
Despite being heavily pregnant with her third child (she gave birth to a boy on December 7), Winslet - who had borrowed the keys to a friend's beach hut for the purpose of our interview - goes out of her way to make sure that I'm comfortable and, most crucially, enlightened. She doesn't speak in carefully prepared soundbites; what she says seems to come straight from the heart.
Winslet's latest film is Labor Day, for which received her ninth Golden Globe nomination (she has won twice). Set in 1980s Massachusetts, it tells the story of a depressed single mother, Adele, and her young son, Henry, whose lives are turned upside down when an escaped convict (Josh Brolin) demands that they give him a lift home from a discount store on the eve of the Labour Day weekend.
It is a gripping tale, mainly thanks to Winslet, who gives Adele enough complexity to make her essentially feeble character, and her consequent controversial decisions, a masterclass in human frailty. For Winslet, playing Adele was a huge challenge.
"I have never really played a character that has considerably more vulnerability than strength," she says. "She felt very alien to me, every day. Usually, I can find something in a character to relate to - Hannah Schmidt in The Reader, for example. I didn't like her and she was nothing like me but she had a certain strength that I could totally latch on to.
"And I do tend to find myself drawn to strong characters - women who are either finding their way out of a situation, looking for love, having some struggle within love, or questioning the big things in life. These are the things that fascinate me."
Director Jason Reitman, whose previous films include Juno, Up In The Air and Young Adult, says of his lead star, "Every time she takes on a role, Kate jumps off the high dive. Plus, she's extraordinarily well prepared - better prepared than any other actor I've ever worked with. Her script had more notes on it than my script by a mile. About everything to do with Adele - her hair, her clothes, the way she moves, the way she talks.'
For Reitman, who adapted Labor Day from the Joyce Maynard novel of the same name, there was no one else that he would even consider as Adele. Which is why, when he first offered Winslet the role and she felt unable to take it on, he agreed to put the project on hold for more than a year.
It was March 2011 and Winslet was, in her words, "an emotional husk". She had just completed a year of back-to-back work, on Todd Haynes's TV mini-series Mildred Pierce, Steven Soderbergh's thriller Contagion and Roman Polanski's Carnage.
Fresh from the announcement, in March 2010, of the end of her seven-year marriage to the director Sam Mendes (the father of her now 9-year-old son, Joe; she also has a 13-year-old daughter, Mia, from her first marriage, to Jim Threapleton), Winslet had thrown herself into her work. "Thank God I could do that, at that time in my life. It saved me but it also totally exhausted me," she says.
Then came Reitman's offer. "I had subconsciously made a commitment to my little world - meaning me and the kids - that I wasn't going to work for a year," Winslet says. "I told him that I hadn't got it in me and he said, 'When will you have it in you?' I said, 'Wow! No one has really asked me that before but, I don't know - a year?' When he said, 'Fine,' I couldn't believe it. And that's exactly what we did. We started filming the following summer and by that time I had met Ned, and he and the children and I spent a glorious eight weeks in Boston together."
Ned Rocknroll. Much has been made of Winslet's marriage to Richard Branson's nephew with the strange surname (he changed his name from Abel Smith by deed poll in 2008).
First, there's the fact that it is the relatively young actress' third marriage. Add to that the fact that she met him while staying on his uncle's private Necker Island - where she was holidaying with her then boyfriend, the male model Louis Dowler and where, most famously, she rescued Branson's 90-year-old mother from a house fire - and you get tabloid gold dust. "Hmm, yes," she says. "My bloody fascinating private life."
And yet the facts are inescapable. She was married, aged 23, to Threapleton, an assistant director she had met on the set of Hideous Kinky (where she learnt of the death from bone cancer of her first love, the actor Stephen Tredre). Less than a year after the birth of their daughter, Mia, in 2000, their relationship had broken down.
In the same year that they were divorced Winslet began a relationship with Mendes, whom she married in 2003. They broke up in 2010 amid rumours of his involvement with the actress Rebecca Hall, his current girlfriend. And then came Ned Rocknroll and their marriage at the end of 2012 in a private ceremony in New York, which their respective families allegedly knew nothing about.
And now, a full 10 years after the birth of her second child, Winslet has become a mother for the third time. "I'm very, very lucky," she says, beaming. "Lucky that I can have a baby at all, at my age, and doubly lucky that I'm not doing it by myself. He's a wonderful man, my Ned, and I'm truly lucky."
"Ned meets the cyclist/camping buddy/'let's climb Everest next' bit of Kate very successfully," says Winslet's old friend, actress Emma Thompson. "They'll probably build a house out of goat poo or something."
While there are no plans to do that - yet - the couple are currently renovating their Sussex home, where they will live with all three children.
In everything she does - both at work and at home - Winslet (who last summer learnt to kite-surf on this very beach, just so she wasn't "the little wifey left behind making sandcastles") is a force to be reckoned with.
"Kate is full-on," says her friend Richard Eyre (who, as well as directing her in Iris, adds that he could take credit for acting as Cupid with her and Mendes). "You don't put your feet up when you're with her. She has an energy and she is demanding, insofar as she wants to be given as much as she gives. Which is a lot."
"I do have impossibly high standards," Winslet admits. "But if I'm going to do something, I want it to be done properly, goddammit." This, after all, is the girl who, aged 16, told her long-term agent Dallas Smith that that was just what he was going to be, whether he liked it or not, and who - so the story goes - sent the director James Cameron a single rose with a card signed "From your Rose" as part of her campaign to land the much-coveted role in Titanic.
Thompson remembers meeting Winslet at the audition for Sense And Sensibility three years earlier. "She was nervous but full of commanding determination," she says. "There was no stopping her."
To understand the woman you need only to look to the girl.
"I feel very fortunate to have made it from there to here," Winslet said in her teary speech after accepting her Oscar for The Reader in 2009 (the sixth time she had been nominated). "There" was Reading, where her maternal grandparents originally founded the repertory theatre.
Her parents, Roger and Sally, were actors who had to take other jobs to make ends meet.
"Dad never had a career that could fund our family in any way, shape or form," she says.
"So he had to do whatever it took to keep food on the table. He worked for a tarmac firm, he was a driver for the National Trust at one point, and he was a postman, too. I remember that time, particularly. I was very little and the only way I could see him before he left for work was by getting up very early in the morning, just so I could be in his world."
For all the moments of hardship, Winslet and her siblings (she has an older sister, Anna, a younger sister, Beth - both of whom are actresses - and a younger brother, Joss) never felt anything less than loved and happy. "We never felt like the poor kids, which is absolutely a credit to my parents. We lived in a lovely terrace house and we all had each other. Still do."
In 1985, when Winslet was 10, her father had an accident on a canal boat in France and nearly lost his foot. "After that he couldn't really act and things got much harder," she says. "He has a great spirit, my dad, but the sporadic acting work that he'd had before the accident definitely became even more sporadic afterwards. I suppose that was when disappointment crept in."
At 11 Winslet won a place at Redroofs Theatre School in Maidenhead and, shortly afterwards, earned her first pay cheque dancing in a Sugar Puffs ad. At 15 she played the lead in Dark Season, a BBC children's science-fiction series. By the time she was 16 (with one A grade at GCSE, in drama), money was so tight that she had no choice but to leave school. "It wasn't simply a case of wanting to succeed," she says. "It was more a case of having to."
Having been teased by her fellow students about her weight (she says at 15 she weighed almost 13 stone), Winslet dieted herself down to 10 stone. Bit-parts on television followed and, in 1992, her fortunes changed when she beat off 175 other hopefuls for the part of Juliet Hulme in Heavenly Creatures, Peter Jackson's 1994 film about the Parker-Hulme murder case in Christchurch in 1954. "God, I was lucky," she says, laughing, "because the thing that I wanted to do was the only thing that I could actually do. The fact that I also happened to love it was an added bonus."
Winslet still loves what she does. "More and more, actually," she says. "Because I know more about the world, more about myself, more about what makes people people now than I ever did. Yes, it's exhausting and hard work and all of those things, but it really does feed my soul.
"It's my little private creative thing and I'm very protective of it. It is also, in a way, a luxury for me. There are several moments on set when I can sit down and have a cup of tea. 'Oh, wow! There's an hour and a half till I'm needed? Bloody hell! Let's do the crossword ..."'
With characteristic determination, Winslet has made her career fit in with her family life, persuading producers to schedule filming around school holidays so that her children can come too. Only once has she done "that thing you'd imagine actors have to do, hauling the kids and teachers and all that jazz on to location", when she filmed Carnage in Paris. "And that's only because spending two months in Paris was an invaluable life experience for all of us."
While her children are young Winslet refuses to work back-to-back. She also, despite much cajoling from just about every great director, has yet to take on a theatre role. "I'm not prepared to miss seven bedtimes a week," she says.
Winslet's double life is a source of great amusement to her. "Waitrose [supermarket], Oscars. It really is that bonkers. But there are things I have to do to counter the fame side of things," she says, suddenly serious. "Like, for example, not going to those restaurants where [well-known] people are going to be, not putting myself in a position where I need to feed my brain with who's who and who's doing what and what's on. Honestly, I push my shopping trolley past the aisles of gossip magazines and I often just go, 'Who the f*** are all these people and what the f*** are they doing?"'
If Winslet's success can be seen as a kind of anaesthetic for her parents' disappointments, it is also a potential wound for her children. "I don't want them ever, ever to think that travelling the world and wanting for nothing is normal," she says. "I used to be terrified that they would get spoilt but actually they are only spoilt if you spoil them, and I don't."
She talks of how they have to save their pocket money to buy anything special they have set their hearts on and of how, in 2011, "we came back to England for the summer and I deliberately rented us a properly tiny cottage to live in. It was lovely, but it was the size of a shoebox. And, do you know what? That was the summer when both of the kids said, 'Do we have to go back to America?' because it was the summer that they felt the happiest."
Only recently, Mia and Joe have begun to realise quite who their mother is, on account of her taking on the role of Jeanine Matthews, the ominously intelligent leader of the Erudite faction in the forthcoming Divergent franchise. Based on the best-selling young-adult trilogy (set in Chicago in a dystopian future) written by Veronica Roth, the films promise to give The Hunger Games chart-toppers a run for their money.
"Suddenly - only just - I'm cool!" she says, laughing.
Winslet falls quiet as she looks out towards a distant peninsula. When she speaks again, she is visibly emotional. "Funny to think that I used to go crabbing just over there on our family camping holidays as a child and now I'm sitting here, on the other side ..."
Prodigious talent, coupled with ambitious determination, has got Winslet to the other side, with more than her fair share of emotional upheaval along the way.
"I don't really do simple," she says, knowingly. "I'm not really interested in simple at the end of the day, because nothing's ever simple and nothing's ever perfect. People certainly aren't - I would hope, anyway, because that would be boring, wouldn't it?"
Labor Day is in cinemas now.