Tony Britton
— Dr. Robert Marriott
Virginia Maskell
— Dr. Lucy Byrne
Ian Bannen
— Alan Andrews
Kenneth Griffith
— Dr Shole
Peter Cushing
— Professor Sewell
Thorley Walters
— Special Agent Prince
Donald Pleasence
— Parsons, alias Bill Brown
Spike Milligan
— Arthur, lab orderly
Raymond Huntley
— Sir George Gatting the Minister of Defense
Sam Kydd
— Slater
Anthony Booth
— Parkin
Basil Dignam
— Dr Childs
Brian Oulton
— Director
Robert Bruce
— Levers
John Payne
— Iverson
Bruce Wightman
— Phil the Barman
Geoffrey Bayldon
— Rosson
Andre Charisse
— Heller
Ian Wilson
— Pin Table Man
Margaret Lacey
— Prince's Secretary
Murray Melvin
— Teddy Boy