We filled up on the K&A last Summer .The marina we used told us that they had a visit from the Revenue the week before. They were a bit put out as all the revenue man did was to flick through the marinas records and say that's fine.
He then explained that all they had to do was to check that people selling fuel were keeping records and there was no way they had the staff or time to chase after boaters who hadn't declared tax. At the end of the day you decide how much tax you pay and I certainly don't worry about it. Needless to say we pay very little.