There are similar laws in America. A police officer is considered to be harassing you if he follows you for an inordinate period of time without a reason. This allows for tailing if you are a suspect or might lead them to a suspect. It does not allow for them to follow you in the hopes you do something wrong. It is the definition of inordinate that is the most difficult to define. In most cases it is loosely defined as the time to get the information on the vehicle back via computer, then the officer must pull you over or let you go.

However I would like to give you the homeland defense version of what to do. If you are worried about being terrorized by an unmarked police car, duct tape over your license plate, carry more duct tape and plastic in the car to seal you in so he can't use any biological or chemical attack to force you out if he does stop you for the minor violation of not showing your lisence