They don't ... and I have now discovered that they haven't
I can more-or-less 'cancel' my OP. Never trust the labels on a CU
. It seems that the guy who did the (re-)wiring was more sensible than I had thought, other than being incompetent with his labelling!
I obviously hadn't actually checked before, but I was now moved to do so, and have discovered that one of the sockets circuits does both middle and upper floors (all bedrooms/bathrooms, so essentially fine), one does just the kitchen/utility and the third one the rest of the ground floor - in other words, probably exactly what I would have done if designing myself.
I therefore think that the present arrangement is fine, and am sorry for having wasted people's time with a non-question
Kind Regards, John