Revealing mistake: The raid took place at Xmas in 1951. In homage to this fact, the characters wear big coats and one of them even rubs his hands together and goes "Brrr." Yet the movie was filmed in the height of summer. Trees in the background of scenes in London are full of leaves, we never see any mist in exhaled breath and the lighting levels and shadows indicate a high, bright sun.
Factual error: As the cars travel over 1950s Westminster bridge, the modern red route lines can be seen on the road.