In this episode we're looking at the British decryption efforts centred around Bletchley Park. I'm sure to some extent you're all aware of the German cypher machine Enigma which proved so challenging to crack, but how much more do you know of British Government Code and Cypher School, which was housed at Bletchley Park during World War II.

Joining me is Dermot Turing, if the name sounds familiar he is the nephew of the now well known Alan Turing whose name is now synonymous with the cracking of the enigma code. Dermot has served as a trustee of Bletchley Park and the Turing Trust, he is author of a number of books looking at Alan Turing and codebreaking, his latest being The Codebreakers of Bletchley Park.