Just a thought. If it is an MOD carpark, all vehicles parked there will have had to have had their details registered with the base in order to be left there. Therefore to contact the owner, write a note addressed to "the owner, reg no, carpark x and hand it in to the "snowdrops" (MP's on the gate or guard room).
Good luck!
By way of intro; Web name Oscar, AKA Guy - founder of Tamar Area Capri Owners (TACO). Keep being carded by OSF members - most unusual carding was on the top level of a private carpark at Heathrow where I left my Brookie when playng with a BA 737 Flight Simulator!!! Daily drive is an anonymous White 2.0 Capri that started life as a Caberet II and was driven by a couple of page 3 girls in London.
This is an excellent site - keep up the good work guys.