Is every card shuffle unique?

Can it really be true that every shuffle of a deck of cards is unique? Mathematician and stand-up comedian Matt Parker claims that every time you do a shuffle, the cards have never been in that order before. But how can he be so confident? Matt came into the studio armed with a deck of cards and some very big calculations to back up his big assertion, and introduced us to the mind-splitting mathematical world of factorials and combinatorics. Presenter: Tim Harford Producer: Nathan Gower Series Producer: Tom Colls Editor: Richard Vadon Programme Coordinator: Brenda Brown Sound Engineer: James Beard