Of course the BSS is RCD/RCR+ There are things in the BSS which are not required in the RCD/RCR - one that springs immediately to mind is CO Monitors/Alarms. Each country is allowed to add 'local' requirements to the RCD/RCR. The RCD/RCR is simply the 'baseline'.

As an aside, I was wrong about the rubbish disposal: it's in a new compound a short towpath walk south. A mention of that on the sign for the sani would have been It useful. The tap at the side is the shutoff for the flush cistern: there is a water supply and it does flush, there's just no way to put water into a cassette. It did occur to me that if the anti-contamination water regs are causing problems, then a flush supply from a valve installed in wall of the flush cistern, close to the bottom, would work fine and solve that.