What made you want to tackle sci-fi again? I hadn’t done sci-fi for so long and I really did enjoy doing it, plus when it comes to the Alien world no-one else had addressed the obvious question. The three films that followed Alien never asked the origin question and I thought that was interesting to tackle. It felt like unfinished business and with unfinished business you never know how it is going to evolve, and Prometheus evolved into a whole other universe. If one wanted to follow through on that you’ve got a person [Noomi Rapace’s Elizabeth Shaw] with a head in a bag [Michael Fassebender’s David] that functions and knows exactly what to do about everything because it’s got an IQ of 350. It can even explain to her how to put the head back on the body and she’s gonna think about that long and hard because once the head is back on his body he’s dangerous.

So that’s the Prometheus sequel? [Laughs] I wish it was that easy. They’re going off to paradise but it could be the most savage, horrible place. We think of it as a wonderful place, but it could be terrible. Who are the Engineers? Where do they come from? Are they so evolved and so ahead of us?

David is a fascinating character… He’s the kind of person that if I handed him Paradise Lost he could read it and then recite it, even though it’s such a thick book. Have you read Paradise Lost? I couldn’t go through four pages. But David could recite it word for word immediately afterwards. He could read the telephone directory and remember it all.

Was it your idea to shoot in 3D? Yes, but it was an obvious thing to do. I may as well join the club, you know? There are directors who won’t shoot in 3D but then there are also directors who will only shoot on film rather than digitally, but they’ll have to change because celluloid is disappearing. The labs don’t exist anymore, except to service the old films. I like the digital process. It’s more reliable. You push a button and you get 5,000 prints that are all absolutely the same, but if I was going to do it physically with film at the end of the process the chemical has gotten so used it’s no longer functioning. That’s why you get different quality of prints; that’s why Stanley Kubrick would have 20 guys sitting through 5,000 prints to check that they were all the same, which they never were. They couldn’t be, given the chemicals in the bath, temperatures, sediment in the bath, so many prints have already been through it so it’s polluted. I would never use film again.

How do you think the film will look on home screens? It can be watched in 2D and it will still look great. And every TV set being sold today is 3D-capable, and on a big TV set it’s fantastic. It’s like having a window in your room and quite marvellous.

Why did you use a lot of real sets rather than full CGI like, say, Avatar? [Laughs] Because it was a quarter of the price of Avatar. Sorry Jim! I’m a cameraman primarily. On Alien I was the camera operator and on The Duellists before that, but I wasn’t allowed to do it on Blade Runner because that was my first time in Hollywood. Then I did Legend over here and was the camera operator on that, and it’s wonderful because you’re not the photographer but you’re working very closely with him. My films have always been criticised for being too visual, too beautiful, too misty, too this or too that, but I really don’t care. We’re dealing with a visual medium; storytelling is entirely visual, as Hitchcock said. And I thought ‘I have an advantage because I have an eye for visuals’ and I’m very fast because I can see what I want, and because I went to art school and I can draw I know exactly how the script is going to evolve into a film. I can see the scene.

Is Prometheus designed to stir up religious debate? It’s a movie, not a science lesson or a religious lesson. And it presents two things: it presents the idea that there is a god and also that there isn’t a god but we were created somehow. If we were created then who created us? We were a petri dish at some point. The argument then is: If this group created us, who created them? Where does the buck stop? The film is supporting the thesis that there may indeed be a god, that there’s a higher being. [Pondering] Who wrote The Bible? During the thousands of years The Bible was put down on paper, who kept reordering it so that it’s now between two covers? A lot of wisdom goes into The Bible, a lot of observation, even to the extent that God created us in his own likeness. If I’m going to be created in the likeness of an Engineer he’s got to be humanoid, but if we’ve been here for three or four billion years… To paraphrase John Updike, what the hell happened in all that time? In the last 75,000 years or so we’ve had massive upheavals – being bombarded with asteroids. What made The Gulf Of Mexico? Did that end the dinosaurs? Why can you find huge sharks’ teeth at 12,000 feet or more? We’re always speculating. The more we discover the more open the book becomes. Have you noticed that? History is being completely rewritten. Were we visited before? I think it’s entirely likely and it’s ridiculous not to believe that we were. We can’t conceive of the idea that there’s a civilisation a billion years ahead of us. We can’t grasp that, that we may be chimpanzees by comparison. Just think: They landed here a billion years ago, left a legacy, and they would never come back because it would take a billion years to evolve but they may visit occasionally to see how it’s doing…

So maybe the movie is saying knowledge isn’t power? The more we try to find out it seems to me we peel away layers of information and we learn more and do extraordinary things, but we’re dis-evolving in other ways aren’t we? We can’t even live together.

How did you settle on Noomi Rapace for Elizabeth and Michael Fassbender for David? I saw Noomi from watching a lot of Scandinavian talent; a lot of great talent has come out of Scandinavia in the last few years, apart from Ingmar Bergman further back of course. I saw The Girl With The Dragon Tattoo about two and a half years ago and when I met the director I asked about this street punk who was in the lead. He said ‘She isn’t like that in real life’ and when I met her I realised she was the real thing, a real actress. That’s how it started to evolve. The screenplay was nearly complete and I thought ‘Why not?’ Of course there was the usual stuff of ‘She’s not well known’ but then nor was Sigourney Weaver. Then Michael Fassbender, of course, is one of the great young actors right now. I didn’t think he’d do it actually because the David role isn’t his kind of thing, it isn’t macho, but then I think that’s why he went for it actually. He’s kind of clowning around and playing an obsequious and dangerous person or creation without malice. I love the scene where David has lost his head and asks Elizabeth for help and she says ‘Why on earth should I help you?’ She realises he’s the only way she’s going to get out of there. If there’s a sequel it’s going to be Elizabeth Shaw with David’s head in a bag and she’s going to keep the body as far away as possible.

Is it a rumour you’ll be making a Blade Runner sequel? It’s not a rumour – it’s definitely happening. With Harrison Ford? I don’t know yet. Is he too old? Well, he was a Nexus 6 so we don’t know how long he can live. [Laughs] And that’s all I’m going to say at this stage.

Prometheus is out now on DVD and Blu-ray (3D and 2D) and packed with special features on the making of the film, and filmmaker commentaries that may help unravel the film's complexities. It is available from all good retailers.