I ended up having a locksmith guy come out and while he was cutting me a key from the lock, the people who live behind where I park my car came strolling out (having seen me manically searching my car all day looking very pissed off) asking if I'd lost anything while dangling my car keys in their hand
Their son had supposedly picked them up in the morning (even though I'd been out there at 730am looking for them and their house was still all dark with no one awake!). I personally think they found them last night and just kept hold of them to worry me overnight beause I had issues with them a year or so ago over them using my parking space.
At least they turned up in the end I guess, and it only cost me £45 for the other key that was cut so not too big a deal. Just a waste of a day when I could have been sorting out my leaking brake pipe Nevermind, all sorted now.