Stephen Sackur speaks to the writer and anti-racism campaigner Matthew Collins. In his youth he was himself a far-right thug, but he changed sides and became an informer. Now he’s a leading activist in the battle against violent extremism. He's written a book - The Walk In - about his experiences. What is the best antidote to today’s peddlers of race hate?

This edition of Hardtalk contains references to racist language.