I can't see why your idea should be any problem and I have to say I've never heard of any problem with carrying some spare in small (yacht) quantities. However the article does make the point that carrying red spare fuel could be a problem, receipt or not and that just shows what a real bu88er's muddle we now have, since we will now have tax paid that is still red after Nov 2008.

My intention is to keep all receipts and stick them in the log, together with notes of engine hours which I do already. I like your idea of carrying the spare (and we carry 2x10l cans even thogh we have never used them!) as white road diesel which can be fed via the diesel car too at the end of the season and replaced with fresh.