This episode is set when Sputnik was launched in 1957 but shows butane lighters which were not in public use until the 1970s.
In the breakfast room, Princess Margaret and the Queen are having tea using Royal Doulton china in the Carlyle pattern. This pattern wasn't created until 1972, however the scene is set in circa 1959.
At the dinner party in Chelsea in 1958, where Margaret and Tony Armstrong-Jones first talk, he points out Ken Russell (Fares Boulos) as doing documentaries for the BBC. Russell did not start working for the British Broadcasting Corporation (BBC) until a year later, since he worked as a freelance documentary photographer until 1959.
The version of "Angel Eyes" by Ella Fitzgerald used was not yet released. Though Ella had released a version prior to 1957, when the episode takes place, the version used was recorded and released in 1960.
When the Queen and Philip are in bed and the telephone rings, it is an American one ring and not the British two ring, and the pitch of the bell is too high.
The darkroom scene with Margaret and Tony is filled with technical problems. The film was never developed, yet Tony made a print from the portrait session they just completed. You develop a print in developer, then stop bath (not water), before fixing the print. The print must be washed in moving water to remove the fixer, or it will turn brown.