Idris Elba knew he had nailed his onscreen portrayal of Nelson Mandela when the famed activist recognised himself in a tiny clip of the film.

The Wire star Elba has stepped into the former South African leader's shoes for his role in new movie Mandela: Long Walk to Freedom, and admitted he was nervous ahead of filming as he had little time to prepare for the part.

But the actor's fears were dispelled when producers showed a brief clip to Mandela and he immediately pointed out Elba, asking, "Is that me?".

Elba tells British GQ magazine, "Game over. So whether anyone else sees this film, I don't care. If I can convince the man himself, that's enough for me."