Stellan Skarsgard has confessed he felt "panicked" by the size of the script for new film Nymphomaniac when he first saw it.

The Thor star appears alongside Charlotte Gainsbourg, Shia LaBeouf, Uma Thurman, Christian Slater, Jamie Bell and newcomer Stacy Martin in Danish director Lars Von Trier's controversial new film about a sex addict.

Stellan, who has worked with Von Trier a number of times before, agreed to be in the film - which features porn actor body doubles having real intercourse on camera - before the director had even written it.

The 62-year-old actor revealed: "He hadn't written the script, he just asked me to make sure I was available a year before we started shooting.

"He said he was making a porno film, and of course I knew when Lars was saying a porno film, it's not a porno film, so I said yes immediately.

"And then when the script came it was like two, three films, it was like a brick, huge and it was like nothing I've seen before in a film script. It's more like a 19th-century novel that when you're reading it you don't want it to end because you like to be in that universe. I thought it was fantastic.

"And then I panicked because the amount of text was more than I've had combined in my entire life before. It was one-and-half-hours of just speaking."

Stellan joked: "I hated having to say so much, I wish I was born 80 years earlier so I could have done silent movies, than have to do so much homework, it was a lot of homework!"

Von Trier's finished cut of the film was five-and-a-half hours long, but it is being released in the cinema in two two-hour parts, Volume I and Volume II.

Stellan plays ageing bachelor Seligman, who meets nymphomaniac Joe, played by Charlotte Gainsbourg, and listens to the story of her life. The actor revealed his character is based on director Lars.

"It's one part of Lars. One part of Lars is the nerd, and everything he talks about from fly fishing, to Bach to Fibonacci numbers, it's everything that Lars is interested in.

"And then on the other side, the character of Joe that is played by Charlotte Gainsbourg, is also Lars. The vulnerable person who is struggling with her sexuality, with life in general, with trying to find a place in society. That is also Lars."

And the actor insisted despite the film's subject matter, Nymphomaniac is the opposite of derogatory to women.

He said: "I don't like the idea of her being punished, because that means there is a higher power that is punishing you, and I don't accept that thought. But she suffers of course from the consequences of her life.

"But she's also a strong woman who stands up for her sexuality and also for herself as a woman. She wants to live her life and she doesn't want to adapt to society, which is always at a price."