"Anyway - sorry to derail the ops thread - best security is to have better security than the landrover down the road from you so they take that one instead!"
Not at all - this is all interesting stuff! And that's exactly what I'm going to do. There's a 1980's Landy 90 Hardtop 'round the corner from me which clearly has a Disc Lock on it. I've seen Disc Locks being whipped off by thieves - same with most Crook Lock type ones also. But they're visual and they're also a visual something - rather than nothing - which is what I have now.
So, I think it's probably going to be a £30 Crook Lock from eBay or similar. And, yes, I realise that they're easy to remove, etc... thanks anyway.