Idris Elba tried to capture Nelson Mandela's "aura" when filming Mandela: Long Walk to Freedom.

The star thoroughly researched his role as the South African civil rights activist and former president - who was imprisoned between 1962 and 1990 for his beliefs - and says his acting was helped by understanding the gravitas he is held in:

"I was more of a journalist than an actor when I first got the role [as Mandela]. I didn't know as much as I'd like to about him, there is so much to learn. Especially about his aura, about the way people feel about him because you can't really act that. You just have to have some understanding of it, so that's what I did. The pressure of taking on someone that everyone knows is insurmountable - ultimately you've got to own it yourself. I don't look like Mandela so I have to ask the audience to come along on a journey and say this is my interpretation."

The Royal Premiere - held in London's Leicester Square - was attended by Prince William, Duchess Catherine, director Justin Chadwick producer Anat Singh and Zindzi Mandela, as well as Idris' co star, Naomie Harris, who told how she met Nelson's wife, Winnie, who she portrays on-screen.

"I found that when I met her she was very warm, very open. She was very open with intimate details of her life which I was really impressed by. In terms of what she asked for in the film - she didn't ask anything. I said to her, 'How do you want to be portrayed,' she replied, 'All I want is for you to tell the truth.' She didn't tell me to play in a particular way, which I was really shocked by and it really helped me," Harris said.

Mandela: Long Walk to Freedom is based on Nelson's 1994 autobiography.