The airliner seen landing at the beginning of the film is a BOAC Boeing 377 "Stratocruiser". It had two passenger decks, with the lower one usually configured as a cocktail lounge. As the passengers deplane, the canopy over the stairs mentioned BOAC's "Monarch" service, which was their brand of all-inclusive first class service.
Inspector Reid:
What are they running down there? An immigration control or a game of hunt-the-alien?
When Steve gets to Kingston House, he enters an elevator with two doors that he has to close manually. In the next shot, when he exits the elevator, there is only one door - the inner gate-like door has disappeared - and it opens automatically.
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