V - V5C
V5C (document) - Otherwise known as the registration document, the V5C is the record of who owns the car and is one of the most important documents when buying or selling a car.
If you are buying, make sure you see the V5C before you buy, and check that the person selling the car is the owner as stated on the V5C. If that is not the case, check that the person selling the car has the right to do so.
Also, check that the vehicle's VIN (see below) and other details match those on the V5C document, and that the form has been watermarked and not tampered with. Since October 2002 it has been illegal to sell a car without a valid V5C.
It is impossible to obtain a new tax disc without the V5C, and you must show the document if you want to get replacement or duplicate number plates for your car. If you don't have a V5C, either because you have lost it or you bought a car without it, you can obtain a duplicate from the DVLA. (See also Logbook.)