Continuity mistake: When the women ride by on horseback in the woods, once they pass the men, they've switched sides. (01:05:38)
Continuity mistake: When Cecily offers cake, the butler puts it in front of Gwyn. In the very next wide shot, there is nothing in front of them, not even their teacups. (01:00:49)
Revealing mistake: When Jack and Algy are singing "Lady, Come Down" to try to get the women to listen to them again, the above shots of Algy playing the piano do not match the music being played. He scarcely even seems to try to make it look real.
Factual error: In the scene where Jack and Algy are eating muffins Jack is wearing a Burberry Check tie. The Burberry Check was not created until the 1920's. The scene takes place in mid-1890s.