Another song, the sweet, lilting Hold On, features vocals from hotly-tipped young British artist George the Poet. It began as a “jam session, me, Ben and Mav, just p------ about, coming up with stuff. And we had a conversation [about] when I spent a night in Robben Island, as an experiment to just understand what it was like to be there. When I think about it in hindsight, oh,” Elba shudders, “it makes my skin crawl.” As part of his thorough preparation to play Mandela, Elba dug into as many aspects of his life as possible. Of course, 27 years in prison were never going to be easy to convey in a film. But in the face of the protests of the custodians of Robben Island – now a shrine and monument to the lives destroyed there in the struggle against apartheid – Elba spent a night there alone, in a cell.