Hmm not 100% sure about this other than ring DVLA/DVLC .
When you look on .GOV website it asks for the 17 digit number on the V5C etc not sure if it can be done through a free hpi report etc if you know someone thats registered etc i will have a dig around when i get a min.
If you get a bad feeling about a car and its history or the perceved owner claiming they aint got the V5 they will post it to you when it arrives excuse etc just walk away unless its someone you fully trust it just aint worth the aggro.
You wouldnt believe how many people try to sell a car that dont belong to them its frightening.
Fell out with the girlfriend but its my car yet its registered in her name with 5k outstanding finance on it and she dont even know hes selling it ffs.
if you have access to diagnostic software like WoW or Delphi you can call up the datasheet & then read the ECU to confirm the numbers match then physically check against the identity plates of the vehicle (not reg plate), pull back carpet/trim edges to check for welding &/or overspray as a sign of tampering with logit numbers