Adaptation Displacement: Very few people now remember the original Colonel Blimp, a pugnacious, reactionary caricature of a retired military officer in a popular newspaper cartoon of the time. Clive resembles him physically (pot belly and distinctive mustache) but is otherwise unrelated.
Powell said that the film was never really about the Blimp cartoons. The original idea came when (then) editor David Lean removed a scene from One of Our Aircraft Is Missing, about a conversation an Old Soldier who tells a young man that he doesn't know what it means to be old. While Lean removed the scene because it didn't fit the film, he did like it and told Powell that he should make a movie around that theme. Blimp was more a general metaphor for Good Is Old-Fashioned then anything else.
Hilarious in Hindsight: Towards the end of the movie, Candy's assistant Murdoch, played by John Laurie, tells Candy that he has joined the Home Guard. Laurie would later join the cast of Dad's Army, which was about the Home Guard.
Values Dissonance: The sequence where time passes between Candy's return from Germany and WWI is shown by him filling the walls of his aunt's empty house with many prize animal heads. At the time, not so much a big deal. But now? A number of those animals are threatened or outright endangered thanks to hunters like Candy. The sound effects don't help.