Kirsty Young's guest is filmmaker and criminologist, Roger Graef.

Pioneering in his chosen subjects and style, for the past fifty years he has shone a spotlight on hitherto hidden areas of society and influenced the entire genre of modern day documentary making. His films on key institutions like the Police have not just helped change attitudes but policy too.

A New Yorker and Harvard graduate, he first came to Britain to study Shakespeare: his London debut as a theatre director was a Tennessee Williams' play. He soon realised that the drama and storylines of real life were where his heart and talents lay.

He says, "What I want on my gravestone is 'Here Lies Roger Graef - he made a difference ...' and people are telling me that I have. But I don't think about it because there's so much left to do."

Producer: Cathy Drysdale.