Factual error: In the scene where Arthur tries to convince Gertrude to not force her husband to "retire from public life" you can see (in the close up shots) that his right ear has been pierced twice which is inconsistent with the time period.
Factual error: The movie, set in the late 19th century, shows in its first shot a naked English lord in bed. On his arm, you can see the scar of a vaccination shot, even though this kind of vaccinations weren't available at the time.
Factual error: Throughout the movie the actors are drinking champagne from gold rimmed fluted champagne glasses. That style of glass was not invented until the mid to late 1960s. They would have been drinking from a Champagne/sherbet glass in the 1890's.
Laura: Then I take it you reject my proposal?
Lord Arthur Goring: I'm afraid I must. For you see, as tempting as it may be, in truth it's little more than blackmail.
Trivia: The play that all are watching when Lord Goring fools around with his looking glass and Gertrude asks Robert what his business with Mrs. Cheevley is, is "The Importance Of Being Earnest" by Oscar Wilde. In the end you see the author coming out on the stage and saying a few funny words. This really occurred at the premier, Oscar Wilde did really say these things. It is a kind of play in a play, as "An Ideal Husband" was also written by Wilde.