When I watch US cop shows or those "World's Wildest..." videos I often hear them say that the car has "expired license plates". Can someone explain what that means please? In the UK registration plates on the car don't expire, but car tax (displayed on a disc on the windscreen) has to be renewed periodically. Is it a similar idea? I've wondered about this virtually every time I've seen it on TV, so if someone could explain that would be great!