Just in case you've been wondering where Timothy Leary's ashes are, they're in Beverly Hills, resting in Tony Scott's loo. You might be asking how the ashes of an American 1960s drug guru wound up in the loo of a British director living in Hollywood. (They were close friends for 15 years; Leary made him executor of his estate.) You might be wondering how it fits with what you know of Scott. If you can't answer, there's a reason. Tony Scott is a man known for two things: being the director of Top Gun and as the younger brother of Ridley. But other than that, who is he? Preparing to meet him, I looked around for clues. There are none.

With no interviews in the archive, I hoped a sense of who he is could be gleaned from his work. A private Tony Scott film festival followed: The Hunger, Days of Thunder, Crimson Tide, True Romance, Enemy of the State, Spy Game, Man on Fire. They're all visual amphetamines - ultra-masculine and thrilling to watch. He is a champion of the alpha-male construct, and though critics complain that he offers only style and no substance, the fact is, he takes chances. He is an exciting storyteller, who enjoys breaking down the DNA of dangerous characters. But as I leave for my visit to the set of his new film, Domino, the DNA of Scott is still a mystery.

We meet in the "valley of fire". Sort of. A complicated shot has gone awry, brows are furrowing and teeth are chattering as the sun goes down, and panic sets in. It's early December and the Nevada desert is a spectacular location. Fifty miles northeast of Las Vegas, jagged mountains of eroded sandstone appear out of nowhere, their fiery colours kindled by the sun. I talk to the cast and crew. Describing Scott, several descriptions come up again and again: fierce work ethic (one day off since August); loyal (same crew every film); incredible stamina (sleeps three hours a night); and shy. Shy? Tony Scott - cigar-chomping, Porsche-driving gatekeeper of celluloid testosterone - is shy?

I glance over. He is sitting on an upturned applecart, wearing his everyday uniform of shorts, fraying vest, hiking boots and faded pink cap, eating his everyday lunch of tuna-fish sandwich, conversing quietly with his producers. Suddenly, shy doesn't seem so far off. But a fellow Brit, Keira Knightley, who stars in the film, has a different view. "Tony loves taking the piss out of people, and he's so charming, he can carry it off. Not all Brits can. His biggest piece of direction to quite a few of us has been, "C'mon - nasty bitch - nasty! You're a nasty bitch!" A lot of directors, if they said that, you'd be like, "What the f***?" But Tony says it and it's like, "Yeah, I'm totally with you!" He'll say to me, "Get your f***ing ugly head out of the f***ing way," and I never take it seriously." If I looked like Keira Knightley, I wouldn't take it seriously either.

On set, Scott is an energetic leader, distinguished by his unrelenting work ethic. He gets up at 3am, makes three pots of espresso, has a cigar, and storyboards every frame of film. Even his body is like a machine. At 61 years old, he is sturdy and fit, wearing shorts that reveal athletic calves. When he's not shooting, he runs every day and spends weekends rock climbing. It's not surprising that he has a low tolerance for laziness. Off set, Scott is still an unknown quantity. I depart from Nevada without the interview, and while that's probably due to time constraints, it seems possible that it's something he's relieved to avoid. Six weeks later, shooting is over and editing has begun.

I wait at the editing facility in Los Angeles and discover that 10 days earlier, Scott underwent a hip replacement. Four days after the operation he was back in the editing room. A special chair was delivered to elevate his legs.

The door opens and he appears: pink cap, same shorts. Only this time he's on crutches. He introduces himself, leaning on one crutch to shake hands. The sound of his voice is distinct, a warmer version of Tom Waits - low and scratchy, with a schoolboy's impishness. He suggests we go to the other room, an office, for lunch.

Tuna-fish sandwiches sit on paper plates on the desk he sits behind. He explains that, during shooting, he was being given epidurals for the pain. His children, five-year-old twin boys, wanted to see the bone after it was removed - it's currently being polished and mounted at the taxidermist. "It's the perfect shape for the head of a walking stick," he says, smiling. "My boys love it."

He pauses. "Is this interesting to you?" This is a question he will repeat several times over the course of the interview; and when I nod, he'll seem genuinely surprised.

The physical pain he's been in would sideline most people, but he dismisses his ability to work through it.

"I love what I do and I've always pushed myself to the edge. I have a lot of energy. Besides, I fight my way through pain - the work gets me through it." He attributes this to growing up in the north. "It's a very depressed part of England. Bleak. That's what I grew up with." Was his childhood bleak? "Nah - we had a great childhood. There were three of us. I had another brother, Frank, who was 10 years older than me. He died of cancer." So how does someone growing up in the north end up as one of the most successful film directors in Hollywood? Did he always dream about making movies? "No, my 'leisure time', as they say here, was spent rock climbing. You go from these big industrial towns and in 15 minutes you're on the Yorkshire moors. Ridley's always had a big influence over me. As a kid he was always drawing and painting, so I wanted to too. There were three things - art school, rugby and girls."

He tells of coming from an upper-working-class family, in which Dad always encouraged them. Rid was the first one who said, "Dad, I want to go to art school". Then, seven years later, I said, "Dad, I want to go to art school". We got scholarships, and we supported ourselves. He went to Sunderland Art School for four years, and then on to Leeds College of Art & Design. Performing arts were emerging as a new art form; there was also a big influence from New York, with the Warhol era. People were reaching for something different. Ridley was at the BBC and Tony was taking photographs.

What was the origin of these sensibilities? It's not like he came from a family of artists. "No, nobody knows where it came from. My dad sometimes did watercolours - though they were very naive. His hero was Winston Churchill." Scott says it was mainly Ridley who inspired him. I wanted to be a painter so badly. I never felt I could make it, even though I got a scholarship to the Royal College of Art - and then made a film for the British Film Institute. Ridley gave me an Ambrose Bierce short story and said, "If you're interested in doing a film, see if you can beg, borrow or steal a Bolex camera." And he got me bits and pieces.

With so much symmetry between the brothers, it begs the obvious question of how they are different. Tony thinks for a while, and looks as though nobody has ever asked him this before. Given that he never does interviews, maybe nobody has. Either his silence means he's thinking of how to finesse his answer or, more likely, he's simply thinking of an answer.

"Ridley makes films for posterity," he says. "His films will be around for a long time. I think my films are more rock'n'roll. I experiment more. Rid was always very classical, whether it was paintings or film. Whereas, as a painter, I was always more interested in Rauschenberg and Francis Bacon." The tone and darkness of Bacon was reflected in the mood of his first film, The Hunger. Now it's considered a cult classic, but when it first came out, it wasn't well received. "Hollywood hated it, and they were right. It was a weak story. It was a vampire movie, and I tried to make it into something esoteric and sophisticated."

After that, his vision shifted. "After The Hunger, the only guys who had faith in me were Don Simpson and Jerry Bruckheimer, who said, "This kid can tell a story.'" He stopped and started three times with Top Gun before committing to it. "I struggled. I wanted to make Apocalypse Now on an aircraft carrier, and Don and Jerry said, "No way.' Then I got it. It's rock'n'roll stars in the sky, silver jets, good-looking guys. I got a Bruce Weber book, and there was one photo where I saw these three characters sitting in this convertible, and I thought, I get it. I know what I can do in the context of what these producers want. It was a challenge. It was fun. It was rock'n'roll."

Top Gun grossed nearly $345m worldwide, and turned Tom Cruise into a superstar. Val Kilmer also gave a memorable performance, in his role as Iceman. "Val was great," Scott recalls. Seven years later, Kilmer was Elvis in True Romance, a film Scott admits is his favourite: "I love the fact that I've done all these different paintings," he says, referring to his movies. "The canvas is the script. You colour with casting, the location, the wardrobe and words, and the centre of the canvas for me is the actors." When asked what the common thread is in all of them, there's a pause. "I still think the way I thought when I was a painter. I like to find different ways of expressing darkness and humour."

There are storytellers like Martin Scorsese ("One of my gods", says Scott), who work from the inside out and draw from their own experience, but Scott draws from the world around him; he's working from the outside in. He draws from other people's experiences. He mentions darkness a lot. Where does this fixation with darkness come from, if not from within? "I look to other people to find it. All around us was darkness when we were younger - rain and the industrial moors. That's where Ridley got Blade Runner from. There was a lot of darkness in Leeds at the time I was at art school. It was the hub of all the drugs coming in from Thailand, and a lot of guys became drug casualties. I have a tendency to gravitate to people who've seen the dark side. They become inspiration for me."

He now has two sons of his own, and their life in Beverly Hills is very different from his childhood in working-class England. They've never seen where their father grew up. Does he wonder how his success will affect how he's raising his children? "They're spoilt. Rid and I had a brilliant upbringing. We went through hard times, but my parents were always there for us. The centre of our lives was the three of us boys: the brothers. But my kids now - I give them everything I ever dreamt of as a kid. They've just turned five and they've got go-carts that do 40mph. They've got motorcycles; and at three years old they were scuba diving in the Pacific. They got to see sharks and manta rays. My childhood was all happy memories. My relationships were spawned through sport. We played rugby, went rock climbing, hitchhiked to the Alps every summer." He's proud of the fact that last year he climbed El Capitan in Yosemite National Park. It is 3,500ft high, and the climb took him three days. "Rock climbing today is a surfing mentality in a vertical world." He admits he is an adrenaline junkie, who gets off on fear and needs to go from one thrill to the next. He is in constant motion - whether it's making movies ("big paintings") or commercials ("little paintings") or climbing mountains. "Fear is my drug. I look for fear. I look for Mexico City at 11 o'clock at night."

Scott has been married for 12 years; it's his third marriage. He says his marriages have all been dictated by changes of career. "My first wife was a painter. I started living with her when I was 19; we got married when we were 23 and then divorced at 29. She went from being a painter to head of production design at the BBC. She stepped down so she could do movies." His second wife was a producer of commercials. "I was with Glynis for 10 years. She didn't really like LA." It's been rumoured that the marriage ended when Scott had an affair with Brigitte Nielsen, who he directed in Beverly Hills Cop II. "All of my women were fantastic." Donna, his current wife, is an actress from North Carolina. When I ask him what he thinks the most difficult thing is about being married to him, he answers without hesitation: "I'm a workaholic and not around very much." Plus the cigars: when he's shooting, he smokes 12 a day. "Yeah, it's disgusting. But it's a worry stick."

One thing he never imagined was going through life without having kids: "It's like never having had sex. Or never having had a dog. And it's funny: it's an absolute f***ing nightmare because my time is so precious, and then there are these two little faces looking at me. The first two years, I'm going, "Ah, shit, what have I done?' Because I walk them every morning, I put them in their trolleys and do a mile loop. And I'd take them and the dogs, and they'd look at me and they'd go, "Mummy! Mummy!' And I thought, "F***! There's something wrong here! I've got these two millstones.' But then from two on, it was, "Daddy, Daddy, Daddy,' and I started to engage them and take them places. I take them rock climbing and skiing - they ski like f***ing maniacs."

A general perception in the film industry seems to be that Ridley Scott is respected, but Tony Scott is loved.

This could be due to his self-deprecating nature. He calls The Hunger: "a total knock off of Nicolas Roeg's Performance". And about True Romance, he says: "It's stolen blatantly from [Terrence Malik's] Badlands. I never try to hide it. I'm the best plagiarist in the world. I steal from the best. I like to call it homage."

He says he knows he is thought of as a commercial director and he won't care if he never gets an Oscar: "Everything I do is very solid. We always get the money back, plus. I shouldn't be saying this, but I think what's most important to me is that people pay me and give me the budget to support my habit, which is trying to touch different worlds and show people these worlds." Why shouldn't he say that? "Because people want to hear that all I want to do is make a commercial movie." Wasn't it a desire for commercial success that made him come to Hollywood? "What made me come here was that in the 1980s, private enterprise in Britain was not supported. There was apathy and resentment towards success."

Scott's success has made him one of the wealthiest men in the British film industry. He owns three homes but not one is in Britain. Two are in California and one is in North Carolina. Will he ever move back to the UK? "Nah, not now my mum's died." In 2001, Elizabeth Jean Scott passed away and, since then, Tony hasn't been back as much. "Ridley and I were great sons. My mum used to wait for the visits. Every year, we'd take her on holiday - her and her friend. We'd take her to Italy and Spain, me and my wife. Just the four of us. My mum was a miner's daughter. She was 4ft 9in; tiny, strong, wilful and determined. She'd look forward to that trip every year. My mum went from working-class northern England to being like Princess Di or the Queen Mother. She finished her days in an Elizabethan house in Hampstead. Ridley's house."

He and his brother talk every day. Together they own two commercial companies. Ridley Scott Associates has been going for 37 years; they are in the midst of 20 projects, and they're co-owners of Pinewood Shepperton studios as well. "Rid and I, in terms of business, are the best team.

He's a killer when it comes to sitting and talking with merchant banks and stuff. I, on the other hand, am there more on a day-to-day basis in terms of the personnel." Is there ever competition? "Ridley loves to see me do well and I love to see him do well." Once, they came head-to-head on something - a Pancho Villa project. But he says that overall they gravitate to different material. "I read Black Hawk Down at the same time as Ridley, and I didn't quite see what to do with it." Talking of Ridley and his Oscar for Gladiator, Scott interrupts: "You know, Ridley is also Sir Ridley." And what do you get a brother who has been knighted? "I got him a 1940s envelope opener which is a sword." And for the Academy Award he got him a framed still from Ridley's first movie, Boy and Bicycle. "Our dad was the grip, Mum was in it, and I was the boy on the bicycle when I was about 14. So I got him a picture of it. I was proud that I thought of it, and it said: "We've come a long way."

There's a knock on the door, and Scott is surprised to discover we've been talking for three hours. He insists on walking me out, despite the fact that it's down several flights of stairs, which he approaches rapidly, as though the crutches don't exist. Just as we're about to say goodbye, he asks if I'm interested in seeing where he lives. "It will give you a sense of me a little bit more, I think." He suggests that I come by on Monday at 9am and enquires whether I'd like coffee or tea, rolls or a danish. When I tell him I'll have whatever he's having, he says: "I'm having cigar."

On Monday morning, gates open up to a Spanish mansion in the hills. It was built in the 1920s by the actor John Barrymore, and is as close to antiquity as you're likely to get in Hollywood. Japanese koi carp swim in the fountain; terraced garden paths dot the property; the front yard has football netting and a trampoline; there is a spectacular view of Los Angeles, and several flights of stairs leading to the house.

The front door opens into the kitchen - a sun-filled, lived-in hub of activity. There is a collage of family snapshots covering a wall of cupboards. Cartoons on the mounted television compete with the sound of canaries and lovebirds cooing in a corner. The twin boys, Max and Frank, sit with their nanny at the breakfast table playing with toy lorries and eating waffles. Max is the talker, eager to explain the history of Buzz Lightyear. Frank is silent and looks like a mini-Tony. A few minutes later, Donna, Scott's wife, comes in, offers me a cup of coffee, shows me photographs of the boys scuba diving, introduces me to her yoga instructor and disappears. The boys, not allowed to skateboard in the kitchen, obediently go outside to race their go-carts.

Scott appears and suggests that he takes me on a tour. He points out all the original light switches, and talks about the photographs hanging on the wall. One, from the 1940s, is of two boys and a little girl. It seems like it could be the Scott brothers, but he never mentioned having a sister.

"No, that's me," Tony laughs. "My mum wanted a little girl." She dressed him as a girl until he was six. "It's amazing I turned out normal."

There is one of the original Marlboro Men - Darrell Winfield. He is now in his eighties. "Where I grew up, there was a billboard above the school yard, and Darrell was on the billboard." He marvels how all those years later, he was directing him in the Marlboro adverts.

In the enormous sitting room there are photographs everywhere. He singles out one from his wedding to Donna, and holds it up. "We flew 120 people down to Cabo San Lucas for four days. It was a recipe for disaster. All the Brits versus the southerners. It was like Deliverance meets The Likely Lads. That was the wedding."

There is another sitting room with a roman mural on the ceiling. It is of the family, including the three dogs. He likes the kitsch element of it and says that when it comes to art he buys what he loves "not to invest". Throughout the house there is an eclectic mix: anything from 15th-century Guido Reni to unknown portraits.

Upstairs, he shows me the reference library, where he says he sits to get his ideas "and steal". From the master bedroom there is a view of the ocean, a wardrobe filled with 20 pairs of identical hiking boots with bright yellow laces and, as we pass the loo, he points out Timothy Leary's ashes.

The full tour requires going outside and down the path to his office. In here, original clapboards of his films hang on the wall. It's a good-luck thing, he says. "This is where I hide. Early morning I come and hide in here." We return to one of the sitting rooms to talk. He speaks about projects he's got that he's excited about, and the challenges in the past of getting them made.

"Do you want an anecdote? I called Russell Crowe while he was on the set of Master and Commander and I said, "So, Man on Fire?" He said, "Listen, pal, have you seen Proof of Life?" I said yes. He said, "I've been there - done that." And that was it.

He won't talk about the specifics of what's next, but there's a possibility of the combination of Russell Crowe and Johnny Depp on screen together. "I've said too much," he says, having revealed very little.

Tony Scott confesses he is not as wild as he used to be in terms of partying, "a terrible phase".

"I mean getting out there and suck and f*** and drink and go to work the next morning - I'm not there any more. I've got a more balanced life. I have a great life."

If he had to distil his life story, what would it be? "I'm propelled by finding kinks in other people. My whole life I have always reached for excitement. Not just adrenaline. Excitement in terms of challenge. There's nothing more satisfying. I'm driven by the fear of not getting it right. And for me. I'm selfish."

Suddenly, he looks concerned. "Am I giving you okay answers? I've never done an article like this. I never do press." So why is he doing it now? "I'm doing it," he says slowly, "because England's my home. And The Sunday Times is the only newspaper I've ever revered. I've always looked forward to it, every Sunday."

We return to the subject of Hollywood and the industry. He feels his strength is his loyalty and moral commitment: "I think that's how people perceive me. People here have short memories. I reached out to somebody - a major director whose first movie I'd helped get made - and he f***ed me over the past few days." The betrayal seems to have penetrated deeply. "I was asking for some additional time with an editor, and as soon as I made the plea, the director reversed it and made it more difficult for me to get him. He wouldn't release him, and he's got four editors on his film. It's a weird competitiveness. I go out of my way to help people." He says he's never forgotten people who helped him and is forever indebted to Alan Parker: "When I did The Hunger, they weren't sure, because I was a commercials director. Alan stepped in and said, "This guy's great, he can handle it." I'm indebted to him for that. But I did a lot for this other guy - and he burnt me. They're spineless. I got angry. I'm very even-tempered, but when I go, no one comes close to me. It's physical and everything."

Scott also fights for what he believes in. For instance, getting Mickey Rourke in Domino: "People say no all the time and they say it for the wrong reasons. The studio says, "It tarnishes the marquee.' When I hear that, I think, "I will get this guy in my movie." As soon as they say that, I say, "F*** you."

We are interrupted when the phone rings and Scott suddenly realises he's been sedentary for too long. He gets up and informs me he's got to leave right away for a meeting.

Leaving me in the kitchen, he propels himself up the stairs to get to his car, while I watch him and wave goodbye. I'm about to call for a taxi when I notice a piece of paper taped to the wall. It's a note from his doctor, a list of hip-replacement post-op instructions. No 1 on the list: avoid stairs.