Alec Guinness

as Professor Marcus

Cecil Parker

as Claude, alias 'Major Courtney'

Herbert Lom

as Louis, alias 'Mr. Harvey'

Peter Sellers

as Harry, alias 'Mr. Robinson'

Danny Green

as 'One-Round', alias 'Mr. Lawson'

Katie Johnson

as Mrs. Wilberforce

Jack Warner

as The Superintendent

Philip Stainton

as The Sergeant