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)
Lucy Griffiths
Miss Pringle (uncredited)
George Hilsdon
Security Van Driver (uncredited)
Vincent Holman
Station Master (uncredited)
Stratford Johns
Security Guard (uncredited)
Sam Kydd
Second Cab Driver (uncredited)
Edie Martin
Lettice (uncredited)
Jack Melford
Detective (uncredited)
Arthur Mullard
(uncredited)
Ewan Roberts
Constable (uncredited)
George Roderick
Radio Car Policeman (uncredited)
John Rudling
Nervous Man (uncredited)
Leonard Sharp
Pavement Artist (uncredited)
Peter Williams
Detective at Parcels Office (uncredited)
Neil Wilson
Policeman (uncredited)
Phoebe Hodgson
Constance (uncredited)