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

Frankie Howerd

The Barrow Boy

Kenneth Connor

Cab Driver (uncredited)

Harold Goodwin

Parcels Clerk (uncredited)

Fred Griffiths

Junk Man (uncredited)

Lucy Griffiths

Miss Pringle (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)

Peter Williams

Detective at Parcels Office (uncredited)

Neil Wilson

Policeman (uncredited)