- Keeley Hawes
- Self - Narrator
- Jerry Roberts
- Self - Senior Cryptographer at Bletchley Park
- Jack Copeland
- Self - Author of 'Colossus: The Secrets of Bletchley Park's Codebreaking Computers'
- Paul Gannon
- Self - Author of 'Colossus: Bletchley Park's Greatest Secret'
- Frank Carter
- Self - Bletchley Park Advisor
- Richard Youlden
- Self - Bill Tutte's Great Nephew
- Dan Younger
- Self - Faculty of Mathematics, University of Waterloo
- Michael Smith
- Self - Author of 'Secrets of Station X'
- Tony Sale
- Self - Co-founder of 'The National Museum of Computing'
- John Scarlett
- Self - Former Director General MI6
- Michele Mosca
- Self - Dep Director Institute for Quantum Computing
- Bill Tutte
- Self
- Bill Cunningham
- Self - Faculty of Mathematics, University of Waterloo
- Tommy Flowers
- Self
- Keith Moore
- Self - Head of Library and Archive, Royal Society
- Kenneth Flowers
- Self - Tommy Flowers' Son
- Duncan Barrett
- Bill Tutte
