 Ian HunterDetective Inspector Gregory | Detective Inspector Gregory |
 Austin TrevorLeopold Dryden | Leopold Dryden |
 Lilian OldlandJoan Dryden | Joan Dryden |
 Henry KendallRodney Fleming | Rodney Fleming |
 Val GielgudJulian Caird | Julian Caird |
 Peter HaddonGuy Bannister | Guy Bannister |
 Betty Ann DaviesPoppy Levine | Poppy Levine |
 Jack HawkinsHerbert Evans | Herbert Evans |
 Donald WolfitSydney Parsons | Sydney Parsons |
 Robert RendelSir Herbert Farquharson | Sir Herbert Farquharson |
 Gordon McLeodChief Commissioner | Chief Commissioner |
| HHannen SwafferHannen Swaffer | Hannen Swaffer |
| VVernon BartlettVernon Bartlett | Vernon Bartlett |
| EEric DunstanEric Dunstan | Eric Dunstan |
| GGillie PotterGillie Potter | Gillie Potter |
| EElisabeth WelchElisabeth Welch | Elisabeth Welch |
| EEve BeckeEve Becke | Eve Becke |
| GGershom ParkingtonGershom Parkington | Gershom Parkington |
| PPercival MackeyPercival Mackey | Percival Mackey |
 Ivor BarnardJoseph Higgins (uncredited) | Joseph Higgins (uncredited) |
| CCecil BevanPolice Doctor (uncredited) | Police Doctor (uncredited) |
| GGeorge De WarfazForeigner (uncredited) | Foreigner (uncredited) |
 Howard DouglasWeisskopf (uncredited) | Weisskopf (uncredited) |
 Arthur HamblingMan on BBC Reception Desk (uncredited) | Man on BBC Reception Desk (uncredited) |
| VVincent HolmanDetective (uncredited) | Detective (uncredited) |
 Bruce LesterPeter Ridgwell (uncredited) | Peter Ridgwell (uncredited) |
| PPercy RhodesWife's Lover on Broadcast (uncredited) | Wife's Lover on Broadcast (uncredited) |
