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

Kenneth Connor

Cab Driver (uncredited)

Harold Goodwin

Parcels Clerk (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)

George Roderick

Radio Car Policeman (uncredited)

Peter Williams

Detective at Parcels Office (uncredited)