Terry-Thomas as Lord Henry Mayley

Peter Sellers as "Wee" Sonny MacGregor

Peggy Mount as Flora Ransom

Shirley Eaton as Melissa Right

Dennis Price as Nigel Dennis

Georgina Cookson as Lady Lucy Mayley

Joan Sims as Ethel Ransom

Miles Malleson as Reverend Cedric "Daddy Bassy" Bastable

Kenneth Griffith as Porter

Bill Edwards as Bill Murphy

Wally Patch as Fred

Henry Hewitt as Gunsmith

John Stuart as Police Inspector

David Lodge as PC Johnson

Joan Hurley as Désirée Mensch aka D. Mandeville

Peter Noble as TV announcer

Victor Rietti as Dr Harz

Ronald Adam as Chemist (uncredited)

George Benson as Photographer (uncredited)

Tom Gill as Police Officer (uncredited)

Muriel Greenslade as Dinner Guest (uncredited)

Andy Ho as Chinese Man in Pub (uncredited)

Barry Keegan as 2nd Irishman (uncredited)

Kenneth Kove as Man Who Lets Out Police Car's Tyre (uncredited)

Wilfrid Lawson as Walter - Contestant in T.V. Show (uncredited)

Arnold Marlé as Scientist (uncredited)

Edie Martin as Lady in Autograph Crowd (uncredited)

Gibb McLaughlin as Old Man in T.V. Show Audience (uncredited)

Marjorie Rhodes as Lady on Phone (uncredited)

Michael Ripper as J.E. Freeman - Greengrocer (uncredited)

Raymond Rollett as Pub Landlord (uncredited)

Austin Trevor as Minister with Heart Attack (uncredited)

Jerold Wells as 1st Irishman (uncredited)