Naomie Harris says playing Nelson Mandela's wife Winnie in 'Mandela: Long Walk to Freedom' took her to ''some really dark places''.

The 37-year-old actress was emotionally affected by some of the scenes in the new biopic about the late South African leader - who passed away yesterday (05.12.13) - and particularly found it tough to portray Winnie being dragged away from her daughters, Zenani and Zindzi, in 1969 and detained at Pretoria Central Prison.

Speaking to BANG Showbiz at the UK royal premiere of the movie in London's Leicester Square yesterday, she said: ''I think for me the most challenging [thing] was being torn away from my kids in the middle of the night, being locked up in solitary confinement, because to imagine that kind of scenario ... I think it is one of the most inhumane things you could do to someone. It took me to some really dark places to play that.''

Naomie watched footage of people being locked up in America to mentally prepare for the role and this helped her understand the emotional turmoil they experienced.

She explained: ''It was a matter of imagining that and watching footage of people in America who have been locked up, because they still use that as a form of incarceration, and hearing them talk about their experience of what it was like.''

Naomie stars alongside Idris Elba, who plays Mandela, and she sang his praises.

She added: ''He's so wonderful! He's amazing, he's charming, he's such a talented actor and a great friend as well.''

Idris was just as complimentary about Naomie and admires her work ethic.

He said: ''She was amazing, she was really amazing. She was so professional, she was very funny and she works hard. She was very beautiful.''