| Name | Character | Episodes |
|---|---|---|
| Colin Blakely | Lewis Burnett | 8 |
| James Grout | Sam McGuire | 2 |
| Gareth Hunt | Eddie Malone | 2 |
| Peter Miles | Harry Gold | 1 |
| Tenniel Evans | Joseph Blenkinsop | 1 |
| Julian Glover | Joe Denver | 1 |
| Anthony Sharp | Henry Wakely | 1 |
| Barbara Shelley | Louisa Galbraith | 1 |
| Jan Francis | Captain Jane Ashley | 1 |
| Susan Brown | Anna Kreidner | 1 |
| William Russell | Peter Kroger | 1 |
| Tony Jay | Laszlo | 1 |
| Jane Seymour | Laura Burnett | 1 |
| Georgine Anderson | Dorothy Graham | 1 |
| Frederick Jaeger | Hans Deiter | 1 |
| Julian Curry | Simon Hatchett | 1 |
| T.R. Bowen | Michael Preston | 1 |
| Frederick Treves | Gilbert Webb | 1 |
| James Maxwell | Leonid Frengel | 1 |
| Brian Croucher | Sammy Grey | 1 |
| William Lucas | George Pilgrim | 1 |
| Freda Dowie | Jean MacKinnon | 1 |
| Michael Halsey | Gert Hauser | 1 |
| Al Mancini | Joe Shapiro | 1 |
| Peter Halliday | Jean-Claud de Salle | 1 |
| Jenny Hanley | Druscilla Lowndes | 1 |
| Jack Watson | Douglas MacKinnon | 1 |
| Aubrey Richards | Taff - Geraint Jenkins | 1 |
| Ray Smith | Josef Milcjek | 1 |
| Patrick Jordan | Ernest Crichton | 1 |
| David Daker | Piet Hollander | 1 |
| Laurence Payne | 1 | |
| Laurence Payne | James Prendergast | 1 |
| Michael Shannon | Milton Webber | 1 |
| Richard Bebb | Sir Charles Hammond | 1 |
| Michael Coles | Hans Erickson | 1 |
| Bill Mitchell | Harry Friedman | 1 |
| Fred Feast | 1 | |
| Billy Cornelius | Karl Grotzen | 1 |
| Ann Morrish | Margaret Burnett | 1 |
| Richard Shaw | Joe Hennessy | 1 |
| Peter Armitage | Sergeant of the Guard | 1 |
| James Grant | Ian Duncan | 1 |
| Beth Morris | Sue Harrington | 1 |
| Gordon Reid | Willie O'Keefe | 1 |
| Naomi Chance | Jane Cowley | 1 |
| George Mikell | Max Gunther | 1 |
| Frank Wylie | David Larson | 1 |