Dakota Johnson had a butt double for 'Fifty Shades of Grey'.

Dakota Johnson at the Fifty Shades of Grey UK premiere

Dakota Johnson at the Fifty Shades of Grey UK premiere

The 25-year-old actress plays Anastasia Steele opposite Jamie Dornan as Christian Grey in the highly-anticipated raunchy drama and though she admits most of the nudity in the film is all her, there was one scene she opted out of.

She said: "There was a close up of a bum getting hit with a belt. That was not my bum, because I didn't want to get hit with a belt."

In order to ensure the kinky scenes were as realistic as possible, movie bosses hired a "consultant dominant" to advise them on accuracy, as well as carefully choreographing the sex to be as comfortable as possible for the two stars.

Director Sam Taylor-Johnson, 42, told 'Entertainment Tonight': "[The scenes are] really technical and really choreographed because it has to be safe and also done the right way.

"There are a lot of rules and things you need to do the right way in order to stay true to the BDSM subculture. We had a consulting dominant who would be on set to help with exactly how to tie knots and where things are placed."

Despite his own involvement, 32-year-old Jamie thinks his co-star had a much harder role to play than he did.

He said: "For Dakota, especially, she's fairly exposed in those situations.

"She's naked, literally being tied up or whatever it is, and that's not easy. It's not a comfortable environment."

The director and two stars of the film walked the red carpet at the movie's UK premiere last night (12.02.15), where they were joined by E.L. James, who wrote the book it is based on, singer-turned-presenter Jamelia, actress Sadie Frost and TV star Denise Van Outen and her new boyfriend Eddie Boxshall.