Unfortunately this is always the case. But you have to stick to the speed limit or you will end up getting another fine. I was chatting to a policeman, who works in the road safety unit, not too long ago and he admitted car speedometers vary. He said you can do approximately up to 5 miles over the speed limit before you will get a fine. I tend to go by the type of road it is. If it is a slow type pedestrian road I wouldn't dream of speeding because a kid or a cat can easily run out from nowhere but if it is a dual carriageway or motorway I do go slightly over. Obviously be careful on roads with speed cameras.