Update - I got a message from Essex police on my answerphone - just about audible, it was on a terrible line, that sounds like they are asking me to just send the paperwork back so they can 'investigate further'. I think I need to type a covering letter restating what I said when I rang them, and the additional info that DVLA has provided me with - ie the vehicle is not registered at my address, never has been. Unfortunately, they would not tell me the correct address do to data security.