Other mistake: In the 1946 Trafalgar Sq scene, modern double yellow lines can be clearly seen as being blacked out on the edge of the road.
Continuity mistake: After the "car chase" the white car gets put in the barn. When the black car arrives it is covered in mud (so much they have to wipe it off the windscreen) from the dirt track. The white car only has a few specks of dirt.
Continuity mistake: In the scenes in Bletchley (south of England) it is obviously early Spring (daffodils, few leaves on trees), but towards the end of the film, and apparently only a few days later, when a German U boat surfaces off the coast of Scotland, it is clearly high summer, with all the trees covered in leaves. Trees don't come into leaf that quickly, and the seasons are always later in Scotland.
Factual error: Reference the rural scenes. In the 40s, barley fields did not exhibit large perpendicular tracks made by crop sprayers.
Factual error: At the end of the film, Kate Winslet makes her way to the "Adelphi Hotel" in Manchester. The outside of the Adelphi building just off the Strand in London is used.
Plot hole: When the police search the white car and the barn they fail to find the compartment in the car behind the boot in which the decoding equipment was hidden. This is completely improbable. It was a standard car, the compartment was not a secret add on, and the police were supposed to undertake a thorough search of everything.
Continuity mistake: In the scene in Scotland where Puck is rendezvousing with the German submarine whilst being watched by the British security services and police, there are several shots of the sub through binoculars supposedly from the perspective of the British on top of a hill. These views are all (with the exception of the last one of Puck meeting the sub) from sea level.
Factual error: At the beginning of the film, as a British Admiral (or senior naval officer) leaves Bletchley he returns a salute. Although a naval officer, he does not give a naval salute but rather a half hearted army salute.
Other mistake: The last shots of Trafalgar square you can see twice a UPS van driving in the background.
Factual error: Kate Winslet and Dougray Scott drive through a field of the crop, rape. This crop was not grown during the second world war.
Factual error: The scene of 1946 London - Trafalgar Sq. looking south down Whitehall. You can see the turrets of the new MP office building - put up only a few years ago.