Driving through the main gate at New York's Steiner Studios feels rather like entering Guantanamo Bay prison camp. A guard checks your identity and raises the security barrier. Ahead lies a vast car-park that was once a parade ground, dotted with newly built hangars. The similarity with Guantanamo is no coincidence. Though just across the river from Manhattan's famous skyline, the Steiner Studios lie in the old Brooklyn Navy Yard.

Deception, Ewan McGregor's new erotic thriller, is being shot on a sound stage in one of the glass-and-steel hangars, and the Scottish star has a busy schedule ahead of him. Over the next two days, he is to film a montage of sex scenes that requires him to get it on with five different actresses - none of whom he has met before.

The director has left the sex scenes until the last two days of the seven-week shoot. McGregor, looking very American in black jeans, a striped jersey, a baseball cap and baseball boots, seems, if not downright nervous, at least preoccupied with the marathon of sex scenes on which he is about to embark.

“They're interesting. I've done a lot of them. I try to find something about them that is realistic,” he explains. “There are Hollywood glistening sex scenes, and I'm not very interested in them. I don't think they're very interesting to watch... I think sex isn't like Hollywood sex. It's very often many things, but it can very often be awkward. In these scenes, they're strangers, so they can be embarrassing. And things don't just go off like they do in a Hollywood movie. I think finding those moments that make it real makes for the audience a much more erotic experience, or a much more powerful experience, because you recognise things you do yourself, or things that have happened to you.”

Despite his family role as Obi-Wan Kenobi in Star Wars, McGregor has earned a reputation as one of the few male actors who will happily shoot full frontal nudity, dropping his trousers for explicit scenes in Trainspotting, Velvet Goldmine, The Pillow Book, and Young Adam.

McGregor, 35, the married father of three daughters, argues that nakedness is a part of life that deserves to appear on screen. “I'm not inhibited to take my clothes off in movies, because I think movies are a reflection of life, and in life we are naked a lot of the time - at least I am,” he says.

In Deception, billed as a “seductive psychological thriller”, McGregor plays the solitary Wall Street auditor Jonathan McQuarry, who is lured by a flashy New York lawyer called Wyatt Bose, played by Hugh Jackman, into a high-priced sex club known simply as “The List”. He meets and falls in love with a beautiful woman known only as “S”, played by Michelle Williams, who is kidnapped.

“The whole idea about this character is that he is being born. That he is becoming alive having been dead. At the end, there is a line. Wyatt says to him, 'You were dead already, and I gave you life,'” McGregor explains. “In a sense he is right. He suddenly has this glamorous alpha male guy who wants to be his friend. Through that, he makes a step forward out of his detachment. And through the sex clubs, the sexual experience, he is further brought out. And then he meets “S” and falls deeply in love. And it almost completes his journey into being a human being from having been a very detached, cut-off guy.”

As an actor, McGregor found the key to the character in the casual revelation that the auditor was brought up as a single child by his mother, who died when he was 19. “That one line of dialogue did it all for me,” he says. “It doesn't always happen. Always with characters, there are character types you can play. But it's much more interesting to find out why people are the way they are. People refer to him as 'being nerdy', and 'he's a nerd'. It's not very helpful for me to hear. I find it much more interesting not just to play a nerd, but to find out why he's so detached.”

Deception is shot in a noir-ish style - much of it in New York night-scenes - by the first-time director Marcel Langenegger and Dante Spinotti, the Oscar-nominated cinematographer of LA Confidential and The Insider. Langenegger, an energetic, floppy-haired Swiss man in a black T-shirt, blue jeans and boots, is an established commercial and music-video director who has lived in Los Angeles for the past decade. He described making his first feature films as “like running a marathon”. “I was always interested in storytelling. In commercials or music videos you always have a little story to tell,” he says. “If you break down the movie, it also is made out of little pieces. The moment that something happens is actually small. The moment is a brick; a short film or a commercial is a wall; and a movie is a whole house.”

As well as co-starring Jackman, Deception is also being co-produced by the Australian actor, known for his role as Wolverine in the X-Men series. But while McGregor is tense about his upcoming sex scenes, his co-star cracks jokes about them.

“One of the girls rang up because the day had been rescheduled. She rang up and said: 'What's the matter, am I not...?'” “They said: 'No, no, no. The day has just been pushed'. She said: 'I just want you to know I'll do anything, and I'm really flexible'. I said: 'Marcel, I know this is your first movie, but I don't think she was talking about the scene!'”

Deception is released nationwide on April 25

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