 | Peter Sellers als Grand Duchess Gloriana XII / Prime Minister Count Rupert Mountjoy / Tully Bascombe |
 | Jean Seberg als Helen Kokintz |
 | William Hartnell als Will Buckley |
 | David Kossoff als Professor Alfred Kokintz |
 | Leo McKern als Benter |
 | MacDonald Parke als General Snippet |
 | Austin Willis als United States Secretary of Defense |
 | Timothy Bateson als Roger |
 | Monte Landis als Cobbley |
 | Alan Gifford als Air Raid Warden |
 | Colin Gordon als BBC Announcer |
 | Harold Kasket als Pedro |
 | Guy Deghy als Soviet Ambassador (uncredited) |
 | Eve Eden als Spectator (uncredited) |
 | Bill Edwards als Army Captain (uncredited) |
 | Mabel Etherington als Ada - Lady in Waiting (uncredited) |
| Muriel Greenslade als Lady in Waiting (uncredited) |
| Fred Haggerty als Fenwickian (uncredited) |
 | Juba Kennerley als Maybury (uncredited) |
| George Margo als O'Hara (uncredited) |
 | Lionel Murton als American General at the Pentagon (uncredited) |
 | Bill Nagy als U.S. Policeman (uncredited) |
 | Robert O'Neil als Reporter (uncredited) |
| Pat Ryan als American General (uncredited) |
| Stuart Saunders als Sergeant (uncredited) |
| Fred Stroud als Fenwickian (uncredited) |
| John Tatum als American Admiral (uncredited) |
 | Mavis Villiers als Telephone Operator (uncredited) |
 | Fred Wood als Bird Seller (uncredited) |
| Jack Arnold | Director |
| Roger MacDougall | Screenplay |
| Stanley Mann | Screenplay |
| Leonard Wibberley | Novel |
| Walter Shenson | Producer |
| Edwin Astley | Original Music Composer |
| John Wilcox | Director of Photography |
| Raymond Poulton | Editor |
| Gerald Endler | Mechanical Designer |
| Jon Penington | Associate Producer |
| Leon Becker | Production Supervisor |
| Geoffrey Drake | Art Direction |
| James H. Ware | Production Manager |
| Maurice Binder | Title Designer |
| Austin Dempster | Camera Operator |
| Red Law | Sound |
| George Stephenson | Sound |
| Philip Shipway | Assistant Director |
| Pamela Davies | Continuity |
| Richard Marden | Sound Editor |
| Stuart Freeborn | Makeup Artist |
| John Winbolt | Second Unit Cinematographer |
| Anthony Mendleson | Costume Designer |
| Joyce James | Hairdresser |
| Edwin Astley | Conductor |
