Long Beach, California, October 30, 2003. Inside the old Queen Mary, now a permanently docked tourist attraction, a film crew awaits its director.

The original interiors of this majestic ship are perfect for the era being filmed today. The year is 1928. The party scene being shot takes place in a Hollywood nightclub. The film is The Aviator, which tells the story of Howard Hughes's early years. An eccentric billionaire industrialist, Hughes was the first mogul to make a $1m movie. He also dated Katharine Hepburn, Jean Harlow and Ava Gardner, and pioneered aviation before receding into a delusional, self-imposed exile. The director is Scorsese, Mr, or Marty, not Martin. The star is Leonardo DiCaprio.

On set, champagne glasses are filled with ginger ale. Period hors d'oeuvres are set on trays - egg salad on white bread. The art-deco bar is packed with crew and extras - men in tuxes, women in flapper dresses. They chat while the shot is set up. The women are shown how to hold their cigarettes and glasses the way they did in the 1920s; a bartender is told how to pour. Scorsese sits just offstage, watching the video monitor, examining what works in the frame. He is aware of the minutiae of everything.

The first rehearsal is about to begin and DiCaprio arrives. Broad-shouldered and tall, his blond hair dyed dark brown, he is Howard Hughes. Scorsese comes out and his presence is momentous, like the Wizard of Oz emerging from behind the curtain. There is a subtle shift among the extras, as if they're secretly hoping for his attention. Scorsese talks to DiCaprio, then he looks around. The crowd is too neat: they need to loosen up. Wardrobe, make-up and hair appear and they "take it down" - he wants the crowd looking more wrinkled and sweaty; this is a wrap party, a wild celebration in full swing to mark the completion of Hughes's landmark 1930 movie, Hell's Angels.

"Picture" is called. Take one, and shooting begins. The music is loud; DiCaprio says his lines. Take two. This time the music stops mid-scene and the crowd mimes in silence, so the dialogue can be heard. Between takes, DiCaprio has a cigarette. He paces, then sits on a crate as he is fussed over by the women from hair and make-up. He speaks slowly, offers amiable small talk. He can be overheard saying that the hottest place he's been is Djibouti.

Two women dressed as devil girls stand on the bar in red sequined outfits. One of them, impatient for shooting to start again, practises swinging her tail. Scorsese had seen photographs of women in these costumes from the 1920s and decided he wanted some. The budget stretched to two.

A final brush of powder over DiCaprio's nose, a dip inside the corner of his eye, and it's take three. The same thing as before - mimed laughter, the devil girls shimmy, then "Cut!" Scorsese comes out and speaks to the cameraman. Then disappears again. DiCaprio stays focused, motionless, faintly uttering lines of dialogue under his breath. The lights have heated the room. A woman comes over and holds a tiny fan up to his face. He doesn't blink.

On and on they go: take six, take seven. A break for lunch, his main meal. Scorsese only sits down for 20 minutes because "getting energy back after eating" is a problem. Then it is more of the same. The scene is shot from different angles. More rehearsals. With every new angle, the lighting is changed. He doesn't allow distractions. It's all part of his meticulous nature, which includes, on this rare occasion, allowing the journalist onto an otherwise closed set to observe what goes into the process. Finally, the required ambience of excess, elegance and glamour is captured. The emotional, organisational and physical commitment required to achieve this one shot has been astounding. This entire day will amount to less than 30 seconds of film. It's no wonder this movie will cost more than $100m. On and on it has gone, all day long. It isn't over because Scorsese is satisfied; it isn't over because he's got exactly the shot he wants: it's over because it has to be, the schedule is tight. There's no on-off switch with Scorsese.

One year later. It is a brisk November afternoon at an elegant restaurant off Central Park in Manhattan, and the director, named affectionately by one star the "Ever Ready bunny", is expected. His assistant arrives first; she wants to ensure he will be comfortable. Scorsese doesn't frequent trendy establishments and he doesn't seek to be noticed. He's earned the prestige of recognition, but avoids it. You will never hear him say "Do you know who I am?" to get the best table, or read about him in the gossip columns. He is a private man and will want a private table. This is not about exclusivity - he single-mindedly prefers to focus on the details of film-making.

He walks in. At 62, he is pulsating with energy; it fills the room. And he speaks like a machinegun, rattling out words like bullets. His assistant leaves behind a mobile phone so he can keep track of the time. He is told he must be somewhere at three o'clock and he nods. He explains that the phone is new and mainly for his family to reach him. It doesn't ring once: everyone understands he is at work. His fastidiousness extends beyond his work. He is wearing a navy-blue blazer and a custom-made pinstriped shirt with his initials stitched into the cloth just above the belt. His square-rimmed glasses amplify a distinguished look - tasteful and civilised - far from the chaotic "mean streets" of Little Italy in New York, where he grew up. Despite his frenzied schedule, he remains stylish and fresh. He has just finished the mix of the film and is working on the end credits. His next stop is California, where he will finish the colour correction. This part of the job is especially nostalgic for him, as it reawakens a childhood spent watching Cinecolor films. But he is dreading the trip to LA, because the man who has just made a film about a pioneer of aviation has a love-hate relationship with aircraft. "I'm terrified. Hate it. Hate it. I don't like to be bounced in the air. Dropping thousands of feet? But I am attracted to it. The seduction of airplanes, how they look."

So why, after a career that has spawned classics such as Mean Streets, Taxi Driver, GoodFellas, Casino, and Gangs of New York, did he choose the well-worn story of Howard Hughes, the man who built industries but died in dishevelled obscurity, obsessively locking himself away for fear of being infected by humans and bacteria? "Speed," says Scorsese. He relates to Hughes's addiction to going faster, higher, sooner. Scorsese is also a driven man: his foot is on the accelerator as he packs as much information as possible into his mind and work. "What I was interested in was this energetic guy willing to try anything. He was crazy about speed - he wanted to be the fastest man on the planet. He was extraordinary." Scorsese, who relishes sitting alone with his thoughts in a cinema, connected with Hughes's sense of isolation. He also related to the young Hughes's conflict: the near-heroic desire to push back boundaries, handicapped by an obsessive-compulsive insecurity.

Scorsese grew up with severe asthma. Even laughing, he says, could bring on an attack, so he was always told to be careful, which fostered a fear of physical activity. Unable to play sports, going to the movies was his escape. "There was a protective feeling I had in that movie theatre. I wished I could have pushed through the fear the way he did." Scorsese admits he still feels fear, just as he still feels driven.