Hi IO540:
Well that's a relief it's not serious anyway. No, no rain. And it didn't actually come off. Instructor #2 did a walk round at Le Touquet and a visual check on the fuel levels, but did not replace the cap on the port wing properly. I noticed it in flight, that it was at a wrong angle. It could have come off; but it didn't.
But, it was another little slip from an Instructor which I wouldn't expect to be made...
TP