Alec Guinness

Professor Marcus

Cecil Parker

Claude, alias 'Major Courtney'

Herbert Lom

Louis, alias 'Mr. Harvey'

Peter Sellers

Harry, alias 'Mr. Robinson'

Danny Green

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

Katie Johnson

Mrs. Wilberforce

Jack Warner

The Superintendent

Philip Stainton

The Sergeant

Frankie Howerd

The Barrow Boy

Madge Brindley

Large Lady (uncredited)

Hélène Burls

Hypatia (uncredited)

Kenneth Connor

Cab Driver (uncredited)

Michael Corcoran

Burglar (uncredited)

Harold Goodwin

Parcels Clerk (uncredited)

Fred Griffiths

Junk Man (uncredited)