Lots of actors NOT in this film
The Magic Box has often been described as containing "virtually every" working British actor of its era. But just off the top of my head I can think of many prominent film actors active in 1951 who did not appear in this movie. Among them:
Alec Guinness, Ralph Richardson, John Gielgud, Jack Hawkins, James Roberston Justice, Valerie Hobson, Margaret Lockwood, James Hayter, Trevor Howard, Alistair Sim, Howard Marion-Crawford, Joan Greenwood, Nigel Patrick, Wilfrid Hyde-White, Jack Warner, Basil Radford, Naunton Wayne, John Mills, Noel Coward, Margaret Rutherford, Herbert Lom (not Herbert Lomas, who is in the movie), Robert Morley, Finlay Currie, Kay Hammond, Kenneth More, Ronald Squire, Niall MacGinness, Maurice Denham, Andre Morell, Celia Johnson, Michael Gough, Elizabeth Allan, Bernard Lee, Laurence Naismith, Geoffrey Keen, Denis O'Dea, Ann Todd, Dinah Sheridan, Ronald Adam, Ian Hunter...and of course scores of others.
Great cast, yes...but "virtually every" actor in British films at the time? Hardly. These people, and many others, are quite conspicuous by their absence.
Please add any names you see missing.