For many of us, passing our driving test and obtaining our license was a seminal moment on our journey into adulthood. The Queen was denied that moment, although we're sure she got over it. In the entire United Kingdom, the Queen is the only person who is permitted to drive without either license plates or a driver's license.
You probably expect that the Queen is chauffeured wherever she wants to go to anyway, but she has been noted to enjoy driving, and has a collection of luxury cars worth in excess of £10m. She's even believed to have taught her children how to drive. Can you imagine being a police officer on a highway, encountering a car driving without license plates, pulling them over to give them a ticket only to find that you've stopped the Queen when she rolls down the window?