If you're going to do it, do it properly.
 

It seems some guy was clocked at 175mph on the motorway in England. The police prosecuted him, but his brief got him off. He was stopped further along the motorway, and the chasing car caught up with him and booked him. They hadn't kept him in view all the time, and so they couldn't prove that he was the driver at the time they clocked him. :D