How do you solve a problem like Winnie Madikizela-Mandela? Perhaps it wouldn’t have legs as a format for a BBC Saturday-night talent show, but it’s a question that Naomie Harris has been trying to answer ever since she agreed to play her in Mandela: Long Walk to Freedom.

I meet Harris at the Soho Hotel in London on the day before the UK première of the film, which tells the story of Nelson Mandela’s struggles against apartheid.