Looks a great picture, past and present . A nice sunny day on an open road, the jag if real, would be fun, but for practicality the Z , an all around winner.
Yes DVLA is a good place to start, however if it is still available it would be put into a future auction. Google Dvla Select Registatons for their details. A lot of old cars were scrapped along with their plates. Good luck.
TOTALLY DIGUSTING... I really feel for you buddy and hope it comes back in the same condition it left. Will keep my eyes peeled around in Gloucestershire.