Update:
A reccy yesterday proved fruitful - thanks to some help from the original lead who works in the offices opposite we found the sprinty (which does look tidy under the dust and whose bonnet has been, er, cleaned).
An hour later after chatting with a couple of uniformed gentlemen we had traced the owner (not his exact location) and learned that he was fine - just not in Edinburgh
The reason the sprinty hasn't attracted security is that it's a "free" car park - not a public highway and too expensive/risky to tow away!
Anyway, a relief the owner is apparently well.