Patzer

The flag or pennant of the British officer's Staff car is flown upside down.

The opening view of the steam locomotive carrying Kiera Knightley has a sign on the front warning of overhead live wires which at that time had not been introduced.

88 as for Heil Hitler (H being the 8th letter in the alphabet) was only introduced in the late 50's as a cryptic alternative for forbidden use of Nazi-symbolism.

When questioning the Werewolf, he draws a a US Colt 1911 .45 automatic instead of a Webley revolver that the British are issued.

In a scene, a record is shown playing the aria "Mon Coeur S'Ouvre a ta Voix" from Samson and Delilah. It is credited as being sung by Maria Callas (and indeed sounds like her), but no records of Callas singing were issued before or during the time frame depicted in this movie.

At the Christmas party, a background actor prominently seen is wearing a white gown with features - an invisible side zipper, adjustable spaghetti straps - that were not invented or commonplace until many decades after 1946. The overall cut and neckline of the dress look decidedly from the 2000s, not the 1940s.

Rachael has cigarettes on the train in her first scene. In her next scene she smokes and talks about how it calms her nerves. She never smokes again, despite several stressful situations.