At one point, runners in The Derby are shown running right-handed.
Epsom is a left-handed racecourse.
Emily Davison is seen willingly sacrificing herself by walking in the horse track of Ascot and being trampled over by a horse. While she did die like this, her intentions are debated as, among other things, had bought a ticket back to London, as well as ticket for a ball that same evening. Most historians agree that her death was an accident, and she was merely trying to put the suffragette banner on the horse when she was run over.
When the suffragettes are within the Central Lobby of the Houses of Parliament, several railings can be viewed on the windows in the background. These were not added to the windows until 1917, 5 years after the film is set, in tribute to the suffragettes who chained themselves to them in 1908. The railings used to be situated in the Ladies Gallery of the Commons but were removed so as to prevent similar political protests at the time.
The film shows police Inspector Arthur Steed speeding towards Epsom Race Course in a 1912 De Dion Bouton 8hp Torpedo. This brand of Italian motorcar would have been,probably, too expensive for him to own personally or the British government to purchase for use by an ordinary government official.
When Maud seeks out her son in the street after her husband has banished her, George spots her and runs up. She scoops him up into her arms and we see the soles of his shoes, which have modern plastic soles with the maker's embossing on them.
The first time that Brendan Gleeson interviews Carey Mulligan, Brendan's hands are resting on the table between them. You can see the watch on his left wrist, visible under his cuff. Wrist watches did not become popular for men until during/after the Great War (1914-1918).