Continuity mistake: In the scene where Guy enters Bruno's house to kill his father, Guy takes out a flashlight to look at Bruno's map. In one shot, you can only see the map, and the light is very small and circular, but in a wider shot of Guy's upper torso, the light covers most all of the map.
Continuity mistake: Early on in the film Alec Guinness is travelling in the back of a van transporting gold bars to the bank. He spots what he believes is a suspicious car following and asks the driver to stop to check it out. The next shot shows the van stopping outside a row of buildings in a London street. The driver gets out to let Alec Guinness out of the van and they are now parked by a low wall with an open vista (probably one of the many bomb sites in London at the time) and no buildings.The next shot then shows the van outside the buildings again.