Factual error: During the scene when Harry and Hagrid are on the motorbike going through a tunnel, the bus signals that it is going to Dartford. Both of the tunnels at Dartford carry north-bound traffic, going away from Dartford - all south-bound traffic, towards Dartford, travels on the bridge (visible in some shots). No traffic enters the tunnels heading south-bound towards Dartford.
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Suggested correction: During times of high winds, the Dartford Bridge is closed, and one of the tunnels does, in fact, carry southbound traffic.