Director Michael Winterbottom has confessed he did not know who Cara Delevingne was before he auditioned her for his new film, The Face Of An Angel.

The 22-year-old British model and socialite - whose face currently adorns billboards all over the world - appears in her first major big screen acting role in the movie based on the Amanda Knox trial, co-starring Daniel Bruhl and Kate Beckinsale.

Set in Sienna, the story follows a fictional case of an American student on trial for killing her British flatmate, but is directly based on the murder of Meredith Kercher, to whom the film is dedicated.

Cara plays British student Melanie who befriends film director Thomas while he is researching the case.

Winterbottom said: "I didn't really know who Cara was, to be honest. Someone had told me who she was and I met her.

"She had just got off an overnight flight from the Caribbean and she was full of energy and she was incredibly spontaneous and funny, and I thought she was perfect for the part.

"Melanie represents energy and joy and happiness and joy in life, somebody who appreciates life."

But The Trip director insisted Cara was not just being herself in the film and she had shown great promise as an actress.

He said: "Cara's great because of who she is, she was Melanie for me, but that doesn't mean to say she's not acting. It's a difficult skill to bring that kind of spontaneity to a film. And she was great.

"Cara wants to act. I think she can act. Being a model is a different skill to being an actor. She makes you feel like she is a 21-year-old student, and it was that side of her when I met her that felt like that anyway. And when we came to filming she was able to convey that.

"She was great on set, she was fantastic with the other actors and she really has a genuine ability to act on screen."

The Face Of An Angel is premiering as part of the BFI London Film Festival at the Odeon West End in Leicester Square tomorrow night (October 18).

Winterbottom said: "It's great to show it in London. I hope I still feel the same way after the screening."