Strange story indeed £19k cossie stolen, no insurance claim, spotted some time later for sale, police reluctant to get involved. just does not sound right to me.
If you wanted the car back so badly you could of made a claim and agreed with the insurance co that if the car is ever recovered at a later date you would pay them the market value of the car as recovered providing the car is still eligable for road use.
The thing with the vin still the same baffles me, car theif steals nice cossie, sells cossie on with no logbook and original floorstamp, new owner no hpi no paperwork buys car, claims it was built up over time and its his car. (surely the original i.d. would have gone by now)
Assuming the current owner has a logbook for the car and dvla don't have it on the registar as stolen it seems to be his car.
The other strange thing is if when it was stolen you reported it to the police and got a crime number did you ever tell them or dvla that you never found the car so can it be registered as stolen not recovered making the vin useless.