According to The Guardian, Mills commented that it was "11AM on a Sunday and the road was completely clear", so the circumstances might not have been completely unreasonable for the DMC to attain such a speed. It wasn't a wet supermarket parking lot with terrorists chasing him in a Volkswagen bus, at least.
Happily for Mills, the case was thrown out as the two ticketing police officers failed to appear before the court. Except for the attention of Her Majesty's finest, Mills enjoys turning heads in the stainless-steel cult car. He's a car fan and clearly a bit of a movie buff, but as there weren't any burning tire tracks left on the motorway asphalt, it's obvious the car in question lacks the optional Dr. Emmett Brown Industries Time Travel Adventure Package.