Every driver is expected to know and understand the speed limits of the road they are driving on. If you are caught speeding, then simply saying that you didn’t know the speed limit or thought it was higher is never going to get you off the hook.
During your theory test you will be asked a number of questions relating to speed limits but it is easy to forget these, especially if you have been driving for a number of years. If you get caught speeding, dependant on the circumstances, you may be asked to attend a speed awareness course. These courses are not deigned to tell you off or to upset you but they are designed to refresh your memory and teach you ways to work out speed limits on any road in the UK. They will also challenge why you speed and help you come up with ways to avoid it in the future.