Suspect

Tony Britton

as Dr. Robert Marriott

Virginia Maskell

as Dr. Lucy Byrne

Ian Bannen

as Alan Andrews

Kenneth Griffith

as Dr Shole

Peter Cushing

as Professor Sewell

Thorley Walters

as Special Agent Prince

Donald Pleasence

as Parsons, alias Bill Brown

Spike Milligan

as Arthur, lab orderly

Raymond Huntley

as Sir George Gatting the Minister of Defense

Sam Kydd

as Slater

Anthony Booth

as Parkin

Basil Dignam

as Dr Childs

Brian Oulton

as Director

Robert Bruce

as Levers

John Payne

as Iverson

Bruce Wightman

as Phil the Barman

Geoffrey Bayldon

as Rosson

Andre Charisse

as Heller

Ian Wilson

as Pin Table Man

Margaret Lacey

as Prince's Secretary

Murray Melvin

as Teddy Boy