Steven Mackintosh as Himself - Narrator

Brian Deacon as Gordon Welchman (voice)

Rosamund Welchman as Herself - Gordon Welchman's Daughter

W. Gordon Welchman as Himself - Ex-Head of Hut 6, Bletchley Park (1939-1941) (archive footage)

Sinclair McKay as Himself - Author, 'The Secret Life of Bletchley Park'

Jimmy Thirsk as Himself - Veteran, Hut 6

Asa Briggs as Himself - Veteran, Hut 6

Jane Fawcett as Herself - Veteran, Hut 6

Tony Comer as Himself - GCHQ Historian and Former Analyst

John Naughton as Himself - Vice President, Wolfson College, Cambridge (as Prof John Naughton)

John Scarlett as Himself - Chairman, Bletchley Park Trust, and Former Chief, MI6 (as Sir John Scarlett KCMG OBE)

Jennifer Welchman as Herself - Gordon Welchman's Granddaughter

Robert R. Everett as Himself - Former President, The MITRE Corporation

Eric Ellingson as Himself - Gordon Welchman's Colleague

Larry Hill as Himself - Gordon Welchman's Colleague