Jamie Dornan thinks 'Fifty Shades of Grey' is ''groundbreaking''.

The 32-year-old actor - who stars as Christian Grey in the erotic film - has admitted that the film's particularly sexual nature is a new thing for mainstream cinema after watching a rough cut of it before the festive period.

He said: ''This kind of sex - S&M - hasn't been depicted on the big screen ever. That, in itself, is groundbreaking.''

Meanwhile, Jamie also revealed that he read all three books in preparation for the film and met with an expert.

He added: ''We had an adviser in the field that we'd talk to, a guy on the kink scene. He's a guru, and a dominant.

''We had some good chats with him. And then there was the practical side of things. How do you use this? I've never held that! I learned all sorts of tricks that will support me through my life.''

Despite being taught the ''practical'' side of things, Jamie joked that he struggled with mastering the technique of using a whip, comparing it to fly-fishing.

He shared: ''There's probably a technique to using a whip.

''I wasn't talented at it. But I got there in the end. It's really like fly fishing.''

To further prepare for his role, Jamie had to work out for three hours a day and drink countless protein shakes.

He told Variety magazine: ''We had realistic expectations that I'm not going to look like Chris Hemsworth in four weeks, nor did we feel I needed to. Christian is not some monster. He's not a beast.

''I'd set my alarm at 4 a.m., and have [a protein shake] pre-made by my bed. I'd wake up in the middle of the night and drink a chocolate milkshake. My wife [Amelia] wasn't too pleased about that.''