Continuity mistake: Before the party scene, there's a little musical montage where all the occurs can be seen getting dressed. There's quick second long shot of Lord Goring, played by Rupert Everett, placing a bright red flower in his buttonhole. A few seconds later, he's placing a white flower in his button hole. Its really quick but it unmistakably Lord Goring.
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.
Continuity mistake: From a long shot Lord Goring and Gertrude are walking. A man on a bike enters from the right and leans his bike on a wrought iron fence right behind some women. Cut to a mid range shot and the bike has disappeared. (00:34:00)
Lord Arthur Goring: Gertrude, it is not the perfect, but rather the imperfect who have need of love.
Gertrude: You seem to know a great deal about it all of a sudden.
Lord Arthur Goring: Oh, I hope not. All I know, Gertrude, is that it takes great courage to see the world in all its tainted glory, and still to love it. And even more courage to see it in the one you love. Gertrude, you have more courage than any woman I have ever known. Do not be afraid now to use it.
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.