But when he put it back on the pile (in his front garden) he put a BMW pannier box on top to stop the polystyrene blowing away. I mentioned that the pannier was moderately valuable and might get stolen if it was left there, and it then turned out that he'd found it in a skip two years ago and was going to chuck it. Upshot, I went home with a pannier box! It's missing the lock that secured it to the bike but otherwise OK, so I'll probably sell it to someone who has a smashed box and wants to put their own locks on it, and give the money to Cancer Research UK.
later - now listed:
if you know anyone who has a BMW motorbike please mention it to them!