December 7, 1995, Los Angeles.

Today I met [director] James Cameron. Even though I haven't read for him yet, he showed me a model of the Titanic and how they were going to do the special effects shots by using a pen which is actually a tiny camera.. The story is incredible, horrible. One lifeboat only just missed landing on top of another. Some were sent out with 11 people on them and yet so many people drowned. The character he’s considering me for is called Rose Dewitt Bukater, a 17-year-old from Philadelphia who is about to marry a man she can’t love. She’s on this ship, feeling as if she is about to be condemned for life, only to find true love on board the Titanic...

December 27, 1995, family Christmas, Reading, England.

I’ve finished reading the treatment for Titanic. My God! I just saw True Lies and The Abyss: amazing. One of Jim’s triumphs is that, in spite of the action, I really, really cared about those people. I wanted to know what happened in the rest of their lives. I want this part.

January 15, 1996, London.

Leonardo DiCaprio is being mentioned to play Jack [a boy from steerage Rose falls in love with]! He is the actor of the century after what he did in [What’s Eating] Gilbert Grape.

February 26, 1996, Los Angeles.

My first proper screen test. For Jude and Sense and Sensibility and Hamlet I’d done a lot of auditions and reading and being put onto a video tape. But a proper Hollywood screen test! I arrived in the morning and it took an entire day, with hair, costume, make-up, on a sort of set that they’d built up, really working the scenes and doing dialogue to the camera. I think it went okay. My fingers are very tightly crossed.

March 19, on set with Kenneth Branagh’s Hamlet, Shepperton Studios, England.

Oh my God! I’m sharing a room with Tina [make-up artist] in this tiny bed-and-breakfast and my mobile rang at 5am! When I heard Hylda’s [Kate’s Hollywood agent] voice, I knew there was only one reason for her to call at 5am and I was screaming so much I woke everybody up, even Julie [Christie, playing Gertrude to Winslet’s Ophelia in Branagh’s Hamlet] in the next room. Then I had to go to work, where I was in a straitjacket, doing Ophelia’s whole bloody mad scenes! Ken [Branagh] is so excited. He’s so thrilled for me. The best thing is that I’ll be playing an American in something that happens to be a really good story.

June 7, London.

I’m exercising like a freak. How vile. I’ve had to give up my daily swim because of all the red dye they are putting in my hair. Too many chemicals. So now I’m lifting weights and cycling my bum off. Jim has chatted to me about the weird eating habits you get into on a really long shoot. He can tell I’m a bit squirrelly about eating and things like that so he has suggested I should have a routine. Not that he wants me to bulk up like Linda Hamilton did in The Terminator but I must be strong enough for the task ahead. He’s told me it’s going to be tough, it’ll be a long shoot. I’m flying to LA to start rehearsals at the end of August. Two months to no cellulite. Can it be done?

September 8, Interstate 5 South Freeway, heading to Mexico and the set of Titanic.

I’m in a car with this great driver called Patrick on the way to Mexico. We’ve been drinking ice-blended mochas from Starbucks and listening to the blues. It’s a beautiful day, and this is a beautiful drive. The sea is to my right and there isn’t a whisper of a cloud in the sky. The cigar Patrick is smoking is huge and smells divine.

September 9, Rosarito, Mexico.

I’m on my little balcony. All I can hear is the sea and the chug of a little fishing boat going to catch lobsters. The rooms where we are living are really nice, airy and clean, although nearer to Christmas they’ll all be blacked out because from then on we’ll be doing night shoots and sleeping by day.

September 10, Rosarito.

It’s extraordinary what’s been done here. They are building studios, cold-water tanks, Titanic funnels, staterooms, dressing rooms, a production office, a gym...on what was derelict land by the sea. The time spent; the money spent! I’ve been shown my dressing room. People keep referring to "my trailer", but it’s really a room, with a huge TV and a CD player and an enormous sofa and a bathroom with shower. I was welcomed with flowers and a little basket of soaps and eye compresses. I’ve just done 40 minutes on the bike. I’ll do my stomach exercises later. Flabby tummy today. There is so much security here. There are men walking around carrying guns and truncheons. Very weird.

September 12, Rosarito.

Today there was an explosion 200 metres away from where Jim was directing me, Leo and Billy [Zane, who plays Rose’s uptight fiance] in rehearsal. And Jim rushed out and came back saying it was 20 kilograms of dynamite - they are creating even more space to build on and the set is so massive as it is. So they just blew up a whole chunk of land. There are thousands of people working here, cranes swinging against the sky.

September 14, Rosarito.

I’ve been up since 5.45 AM, moved my furniture around a bit and made it a bit more cozy. I am on a mission to get rid of a horrid horsehair seat. I’m very tired and I need to get some sleep. I feel smelly, fat, ugly, talentless and uncommited, frightened, lonely, nervous, mad and we haven’t started shooting yet. If it’s not rehearsals, it’s weight training; if it’s not etiquette, it’s voice coaching. By the end of this film, if it’s not suicide, it’ll be an asylum.

September 15, Rosarito.

It is the night before shooting starts and here I am, all pin-curled up and hungry, ready to go. Thinking about Rose. She was so young. I need to think about her childhood, her youth and find my way through the 17 years of her life. I’ll never sleep tonight.

September 16, Rosarito.

No sleep. This is it: day one of shooting Titanic. I’m thinking in American. Hair and make-up done, and cossie on. My life is not my own and probably never will be - and that’s Rose talking. Spoke to Mum and Dad this morning from my little bed; it was 4am and strange, hot and still.

October 5, Rosarito.

The water in the first tank wasn’t so bad, but now we’ve switched to filming in the massive tank where the water is pumped in straight from the sea. It is like swimming in...the coldest winter in the history of Scottish winters. I bet people will think it’s heated, but it isn’t. I am completely freezing. My dresser has been bugging me to wear a wetsuit, but I can’t. I’d be too aware of it and anyway, my dress is too thin for it. Jim doesn’t want see-through and says this isn’t a wet T-shirt competition, but he does want the dress to cling to me when I’m wet and we’ve done all sorts of camera tests for that. It is so cold, but...it means my reactions are real, I hope! It literally takes my breath away.

October 15, Rosarito.

My dress is driving me bloody bonkers. Storywise, from the point the ship hits the iceberg, I’m in the same dress till the end of the film. It’s layers and layers of chiffon and layers and layers of pain in the arse. It’s supposed to trail behind me in the water like a big long snail, but instead it keeps wrapping itself around my legs and tripping me up in the middle of shots which is driving us all mad. Jim had a brilliant idea. Scissors. How satisfying. Now I look like Bo Peep in just the top of the dress and my bloomers. Fine for close-ups but not exactly glamourous, but who cares. Leo is finding this highly amusing. He would. He’s wearing a suit.

October 22, Rosarito.

Jim asked me what I imagined I was going to be doing when I read in the script that the water came flooding up. I said, "To be honest with you, I only ever saw the story boards. I never saw me and Leo actually doing it." Also, then I was excited about it. I wanted to kind of wait and see. Now I know what it’s like and it’s pretty exhausting.

November 1, Rosarito.

I’ve just done a work-out with Diamond, the unlikely name of the burly black trainer. It no longer feels weird working out at 3am, but I am starting to find it too much. We’ve been shooting at night for weeks now. I get up at about 1 PM and eat straight away so that my food has time to go down before I get into my corset. Mel [make-up artist] brought back some lovely scones from Starbucks over the border, will eat for tomorrow’s breakfast.

November 10, Rosarito.

Apparently survivors said getting into the lifeboats was completely terrifying. They had to step out across a huge gap between the ship itself and the boats. Shooting the loading of the lifeboats is pretty scary for us. Our ship is a replica, almost as big, so we have to step out over - hello! - a massive great big gap! And our gap is considerably smaller than the real gap would have been. Diamond showed up on set today to show moral support. I’ve stopped training because it was all too much, but he’s become a good friend and it is lovely having him around. He’d heard this was a really tough scene for me, so there he was, standing there watching, looking out for me...Very comforting.

November 20, Rosarito.

There’s a section of the ship that moves on hydraulics right up to 90 degrees. It’s bloody high up there, so Leo and I are in safety harnesses and clinging to each other for dear life. In some of the shots we have to lean over the railing and witness stunt people hanging off their harnesses doing falls and God knows what else. Survivors’ reports say that it was a really still night. Strange, because it was really still tonight, too. The stars were amazing.

December 3, Rosarito.

Sarah, my stunt double, was being hit by a tidal wave of water in a corridor today. All in a day’s work for her. How can she be so matter of fact about it when I stand and watch, cringing? She’s really helpful when I do my own stunts, always there with kneepads and elbow protection. "Just bend your knees, just relax and control your breathing." Not so easy in the heat of the moment. I’m covered in bruises. Part of the job. It bloody hurts, though. My problem is I don’t think I’ve done my job properly unless I walk away having suffered. Am I a complete masochist, or what!

December 15, Rosarito.

Day off. Much needed. I’ve been for a lovely swim and now I want to go back to bed. Lucky Leo gets more sleep than me. There’s an extra hour-and-a-half added to the end of every day for my pin-curling. Kay [hairdresser] can do it pretty swiftly. Good thing we are both too tired to chat because half the time I’m asleep in the chair. On screen I have luscious red curls. Off screen I look like a bag lady with my headscarf tied in a bow at the front. So attractive. I think I’ve put on weight. I feel heavy, tired, physically swollen and so lonely without my family.

January 9, 1997, Los Angeles.

I feel revitalised. Christmas back at home was lovely. My brother seemed to have grown a foot since I left for Mexico. The new year brings much excitement and I am determined to be positive, especially as I have a new pair of shoes: very high with two big straps across the foot. New shoes, new walk: proud, tall and confident. I must sleep now - 7am pick-up and still jetlagged.