Sir Ridley Scott starts his day like a CEO. Wherever he is in the world, he's on the phone at 6am, to his offices in London, Los Angeles, New York and/or Hong Kong. If he's in LA, he talks to London for two hours. If he's in London, say, making a movie, he calls LA for an hour in the morning from the back of his chauffeur-driven car, customised to contain the essential fixtures of an executive suite.

When the shoot wraps for the night, he's back in the car, on with LA again. He gets home, he eats, and he's tucked up by 10pm, alarm clock set for 5.30 the following morning. Now 74, he's a great believer in the importance of sleep; he never goes out on weeknights while he's in production. "I'm very diligent about that," he says.

His company, Ridley Scott Associates (RSA), employs 60 directors: commercial, music video and movie directors, of course, not corporate ones. He's a major shareholder and co-chairman of the consortium that owns Pinewood and Shepperton studios. There are currently four RSA-backed shows on television, including The Good Wife and Numb3rs. He's produced four films in 2012, directed one of them, and his next project is already deep into pre-production. At this precise moment, he's busy pulling the promotional strings for what's probably the most feverishly anticipated film of his career: Prometheus, aka "the Alien prequel".

Besides the usual hyperbole that accompanies a Hollywood summer blockbuster, the Prometheus marketing campaign includes three intriguing viral ads, each produced in-house by RSA: a fictional TED talk with Sir Peter Weyland (Guy Pearce), the multi-trillionaire entrepreneur who funds the film's mission to a distant planet, in search of the origins of life on Earth; an advertisement for an eighth-generation Weyland android, 'David' (Michael Fassbender), who accompanies the crew of the Prometheus on that mission; and a clip of archaeologist Elizabeth Shaw (Noomi Rapace) being interviewed by Weyland for a position in that crew.

"I'm involved in everything you see," says Sir Ridley, who might just as well be the model for Sir Peter. In fact, I wouldn't put it past him to have personally organised this press junket at a hotel in Soho. The two of us are eating cupcakes, home-baked by one of the publicists – at Scott's instigation? Not inconceivable. Forget for a moment, if that's possible, his onscreen achievements: the meticulously crafted worlds, the epic stories, the formidable characters like Ripley, Deckard, or f Maximus Decimus Meridius. Off-screen, his career has been driven and defined by money, expert management, and fierce competition. "I'm a dyed-in-the-wool businessman," he admits. If he weren't a filmmaker, Scott would be Alan Sugar.

His directing career began in television during the 1960s, where he helmed episodes of the police procedural Softly, Softly, and a pair of Wednesday plays for the BBC. But he was, he recalls, quickly seduced by what he could earn in commercials: "Fourteen times more than as a television director! I thought, 'There's something seriously wrong here'." Before long, he was making 100 ads a year. "Today, you're thought to be busy if you do 12." The discipline taught him efficiency: he rarely shoots more than three takes of any scene ("Anybody who does 90 takes has a problem"), and he's proud of his capacity to create blockbusters on modest budgets. He brought in Gladiator, for instance, at $106m (£66.5m). "Some people would have spent $250m (£157m), in a heartbeat. Just by sheer inefficiency. Unbelievable. Shocking."

In 1967, he and his younger brother Tony established RSA, and began to represent some of their fellow ad directors. Thus he made money not only from his own ads, but from Hugh Hudson's and Alan Parker's, too. It was fear of being outdone by his frenemies, however, that finally spurred him to sacrifice his advertising income, and develop his first feature film, The Duellists (1977).

"I have a healthy competitive nature," he says. "And Alan Parker and Adrian Lyne got films going before me, the fuckers. When someone told me Alan was doing Bugsy Malone, I couldn't sleep for weeks. Then Adrian started doing Foxes, and I couldn't sleep for weeks again. I thought, 'I'm 39, and I'm never going to get to direct a film'. So I stopped making commercials completely for almost a year and a half to get The Duellists going. It cost me a fortune."

Scott self-funded the screenplay, which was based on a Joseph Conrad short story about two duelling French officers in the Napoleonic era. And when he found a studio willing to produce it, he waived his directing fee to get it made. The financial risk paid off. The Duellists won the award for Best Debut at the Cannes Film Festival, and its director was recommended to 20th Century Fox for their latest science-fiction project. He was the studio's fifth choice, behind celebrated veterans Walter Hill and Robert Altman. They declined the offer. Scott leapt at it. The film was Alien.

Fox wasn't entirely confident about its new employee. After Scott persuaded studio head Alan Ladd, Jr to spend an extra half a million dollars on a new final sequence – in which Ripley (Sigourney Weaver) is attacked by the titular monster in an escape shuttle – he announced that he planned to kill off the film's gutsy heroine.

"I thought that when the alien went for her in the shuttle, he should actually slam his fist through her helmet and kill her. Then you cut to the desk, and a shadow of the alien's head comes over, and the finger of the alien starts tapping out coordinates, with obvious intelligence... But when I suggested that to the studio, they had an executive out there on set within 24 hours, saying, 'You will not do that!'. And I guess they were right, because Sigourney made a great run of Ripley."

The film established Scott's reputation for masterly mise-en-scène. He worked with the designer HR Giger to create the iconic alien, but he had once been a designer at the BBC himself, where, but for a scheduling conflict, he would have designed another iconic species of space monster, the Daleks.

"I wanted Alien to be all about claustrophobia," he explains. "I remember going round measuring the heights of the ceilings, saying to the set-builders, 'I said seven-foot-four, you've got these at seven-foot-six. I want you to drop the ceilings another two inches, otherwise I won't see them in the bloody camera!'. I was always a camera operator in commercials. It was faster – one less person to have to communicate with. So I was the operator on Alien, and I took a camera body on set with a lens and said, 'You're lying! Measure it!'. And they had to drop the ceilings."

This close attention to visual detail, however, led to a perception that Scott was more interested in his sets than in his performers – not exactly an actor's director.

"It's bullshit." He spits the word, along with some cupcake crumbs. "Bullshit. There was this idea that the actors were really unhappy on Alien. But it didn't half work, did it? When has Sigourney been better? When has Tom Skerritt been better? Harry Dean Stanton thanked me at the end of it. I climb into the arena with the actors. I cast really carefully, and then I join the club. If Fassbender says, 'How do you want me to do it?' I say, 'Do you want me to show you?'. I don't care. I'm fearless. I'll fucking do it."

Alien has since been subjected to the ignominy of three sequels, a corresponding decline in quality – and, worst of all, a pair of Alien vs Predator films. Of these, Scott (and everyone else) prefers the first: James Cameron's Aliens (1986). But he maintains his original was the scariest: "Some audiences were so incensed by that kitchen scene [in which, famously, the alien bursts from John Hurt's chest] that they got up and left. It was distressing. I loved that. There are some moments that are pretty distressing in Prometheus. In fact, the last hour is pretty distressing."

James Cameron – who has his own fire engine for tackling blazes in the hills above Malibu, and recently dived alone in a one-man submarine to the deepest point on earth – is one of Scott's closest friends in Hollywood. His other buddies, he says, are his brother Tony, director of Top Gun and a clutch of Denzel Washington action movies, and Michael Mann, whose testosterone-fuelled filmography includes Heat and Miami Vice. Sounds like a pretty macho poker game, I suggest.

"Macho? Tony's very macho. He'll still climb bloody El Capitan; I tell him he's a fucking idiot. But I prefer the tennis court. I've got a knee replacement because of the tennis." Naturally, Scott's friends are rivals, too, and it was a visit to the set of Cameron's Avatar that convinced him to shoot Prometheus in 3D. "I said to Jim: 'You've gone and raised the fucking bar again! I've got to do something about this...'."

The 3D footage shown to journalists on the morning of our interview is genuinely stunning – certainly the best live-action 3D I've seen (the majority of Avatar was CGI). Scott's new movie started life as a straightforward Alien prequel but, he explains, as he developed it with writers Damon Lindelof and Jon Spaihts, they strayed further and further from the source material. The film will, however, reveal the origins of the so-called 'Space Jockey', a giant, skeletal space being found dead at the beginning of Alien. Might he hold the key to the origins of life on Earth? That's what the crew of the Prometheus hope to discover on their ill-fated mission.

The film's mysteries are derived from Scott and co's research into myth and ancient civilisations, and he asserts a genuine belief in their possibilities.

"There's a famous Inca carving of a guy sitting on his back, in a frame, and underneath him is fire. He's wearing a helmet and looking up at the universe. To me, that's a goddam spaceship. A lot of Asian and Indian drawings are obsessed with the notion of fire coming from the skies in the form of chariots or vehicles. There are constant references in Egyptian artwork to a very large figure with a lot of small figures in worship. Is that a pharaoh, or a visitor? Why is he helmeted? The drawings of a head with one big eye: that's a man in a space suit.

"All these things are considered mumbo-jumbo, but they were written about by Erich von Däniken in Chariots of the Gods [1968], and a lot of Erich's shit is now being reconsidered. Scientists are saying: now we know a lot more, we believe we're not the only life-form in the galaxy. I've always intuitively thought that, while everybody was laughing at Erich."

Much has been made of Scott's return to science fiction, three decades after he redefined the genre. After Prometheus, he has a follow-up to his other futuristic masterpiece, Blade Runner, in the works. It will be a sequel, he suggests, not a prequel or a remake – but Harrison Ford is unlikely to feature prominently. "I don't think it'll be Harry [starring]. But I've got to have him in it somewhere. That'd be amusing." In the meantime, he's set to direct The Counselor, a "morality tale" about a lawyer who foolishly dabbles in the drugs trade. The script is the first by celebrated novelist Cormac McCarthy, and the cast list already includes the names Fassbender, Pitt, Diaz, Bardem and Cruz.

In returning to not one, but two, of his best-loved classics, it seems Scott has started to consider his legacy. Not just as a filmmaker, but as a businessman, too. The directors represented by RSA include his daughter Jordan, and his sons Jake and Luke. Jordan and Jake have already made their first feature films; Luke directed the TED viral for Prometheus.

When Scott retires, if he ever does, he plans to hand them the reins of the firm. "It's a family business. They didn't want to be part of RSA originally, but now they are. I told them, 'Fundamentally, it's your company'. If I was an actor, then I wouldn't encourage my child to be an actor, because it's really hard. Being a director is not quite so bad although, honestly, it's nearly as bad. But they decided to follow me."

And what would Sir Ridley, CEO, have preferred them to do? "I'd have loved my kids to have been merchant bankers, or international tax accountants; that would have been terrific."

'Prometheus' is released on 1 June

Sets appeal: The other worlds of Ridley Scott

Alien (1979)

"I like to create universes," says Scott, who is celebrated for his painstaking production design. While filming Alien, he decided the 'Space Jockey' set, and the exterior of the spaceship Nostromo, were too small for his tastes. To achieve his desired sense of scale, he had his two young sons stand in for the actors, both wearing child-sized space suits, to make the sets seems larger.

Blade Runner (1982)

The dystopian noir of Scott's Los Angeles, c2019, was inspired by a number of sources and realised by concept artist Syd Mead to the director's specifications. Scott credited the influence of Edward Hopper's famous painting Nighthawks, and the work of French comics artist Jean Giraud, aka 'Mœbius'. He also said the cityscapes were based on modern Hong Kong, and on his childhood memories of industrial West Hartlepool.

1492: Conquest of Paradise (1992)

For his take on the tale of Christopher Columbus, Scott built working replicas of the three ships the explorer sailed to the New World, then had them delivered to the set in Costa Rica. "Two sailed from Bristol, and one from Argentina. They all arrived the day we started shooting, two hours late. I stood on the quay and said, 'Don't they have radio on these fucking things?' And then someone said, 'I can see a sail...'."

Gladiator (2000)

Scott prefers to build his own sets than use CGI, but Gladiator contained pioneering digital effects. A 52ft-high replica of a third of Rome's Coliseum was built in Malta, then transformed to full size using CGI. Around 2,000 extras were digitally enhanced to make a crowd of 35,000. Post-production company The Mill also created a digital body double for Oliver Reed, to complete the actor's scenes after he died during filming.

American Gangster (2007)

For his biopic of crime boss Frank Lucas, Scott filmed at more than 50 locations in Harlem. Having shot commercials in the same neighbourhoods in the years when the film is set, he was keen to avoid romanticising the district. "I kept being told what Harlem was really like, and I said, 'You say that one more fucking time... I was standing here in 1959, photographing people lying on the street in their own vomit. This is what it was like. Where the fuck were you? You weren't even born!'."