They probably won't fine you then. They usually give you 10% of the speed limit. i.e. 60mph they won't fine you unless you go over 66mph. They do this because the majority of cars have analogue speedos so aren't 100% accurate.
Just wait til you get done doing 93 on the motorway in the outside lane and flashing an unmarked police car to get out of the way lol. Not that I have of course....