Factual error: The field marshal is wearing a revolver to the Derby. British soldiers are only ever armed on duty, certainly not when attending social events. He also wears his Sam Browne outside his shoulder strap instead of beneath it; no officer would do this.
Factual error: Solomon says he killed an Italian soldier in the trenches during the war. Italy was a British ally during WWI. While Italy fought the Austrian-Hungarians, they did not fight in France or Belgium.