I have bought several cars without documents, most rescued from Banger Racers, and have had to get the DVLA vas out in exchange for paying £25 for a new one.
Several people I know have also never received a new document when buying a second hand car from a private seller or dealer and have had no joy from DVLA when asking for it to be sent.... and ended up paying the £25.
Shame they are so quick to send you fines when you post your sorn and it does not get to them....
Also... sure if you went through a speed camera in the car with no V5 in your name it would come back to you rather than the previous owner!! May find out soon as I think I did the other day!!