Factual error: In the scene after Chan and Wilson crash their car into Stonehenge they walk away and the view is of a field and a beautiful blue sky. In the sky you can see an airplane vapour trail up on the left hand side of the screen. There were no airliners in 1890.
Factual error: The first Kinetoscope (arcade of 'personal movie viewers') was opened in 1894 and the first motion picture studio was located in New Jersey. There is no way that they would have known enough about motion pictures in 1887 to go into them, let alone go to Hollywood to do so. And the use of the word 'movie' is at least twenty years too early.
Factual error: Everyone is abuzz about Jack The Ripper. The setting, however, is around the time of the Queen's Jubilee, which was 20-21 June 1887. Jack The Ripper did not become known to the public until September 1888.
Continuity mistake: In the market place fight scene, Jackie Chan uses an umbrella to defend himself. In one shot, he breaks the umbrella edge, bending it out of shape. In the next shot, it looks brand new.
Factual error: Several real-life events are off in the movie's timeline. The movie itself is set in 1887, yet it includes Arthur Conan Doyle beginning writing Sherlock Holmes, although he did so before 1887; a mention of the Savoy Hotel, which was not built until 1889; and many references to and an appearance from Jack the Ripper, who was not active until 1888.
Continuity mistake: When Roy and John are talking about getting Lin out of prison, there is a shot of her looking definitely to her right, the shot then goes behind her and we see that both Roy and John are on her left.
Factual error: In the scene where the English police come to Madame Tussaud's Wax Museum, they are waving flashlights, which are seen when they exit the museum. The film is set in 1887; the flashlight wasn't invented until 1898 (according to About.com).
Continuity mistake: In the final sword fight between Rathbone and Jackie, you can see Rathbone's swords flex along the edge more like rubber than a steel sword.
Factual error: The young pickpocket is revealed at the end to be the actor Charlie Chaplin as a child. The film takes place around the time of the Queen's Jubilee in June of 1887. Charlie Chaplin wasn't born until April 16th 1889.
Continuity mistake: During the fight with the street gang, Jackie Chan is about to jump onto the cloth roof to send a gang member flying away. Watch the first half of the shot (from behind Chan) and the cloth in the section Chan is about to jump into is hanging down in the space between the joists and is very slack. When the shot changes from the front to show Chan jumping and landing into the cloth, the cloth is now stretched tight for his landing.
Continuity mistake: The position of Jackie Chan's sword in the gears of Big-Ben changes between the shots we see. It goes from being almost fully in, to about half in.
Other mistake: During the fight in the outdoor market, while Jackie Chan is trying to use a wooden box to defend himself from a villain, notice that the knife the villain uses bends like rubber as it hits the box.
Continuity mistake: When Chon Wang is spinning the wheel back and forth causing Roy to be dunked into the water again and again, in one shot, the timing of Wang turning the wheel doesn't match up with Roy actually dunking into the water. It is the shot where it happens several times, timed to match the music in the background.
Continuity mistake: When Owen Wilson is climbing the minute-hand of Big-Ben, his legs change position between a few shots.
Continuity mistake: When Roy plunges into the water, there should be pieces of rope around the bottom of the pulley device he is hanging from, but there is none.
Continuity mistake: In the beginning, Lin Wang goes from holding the puzzle box in one shot to holding her father's hand in another shot.
Deliberate mistake: When the platform Jackie and Rathbone are on falls, you can see a shot of a restraint snapping out of the floor. Two cuts later is the same shot, just flipped horizontally.