This socket had been plastered over, presumably when the hose was built, behind a kitchen floor unit. The property had a CU replacement a couple years prior to my work. The 'RFC' had been converted into 2 x radials, as (I expect) the electrician (CU one or original) couldn't obtain continuity, but did not disconnect these legs. I only discovered it, when re-locating the kitchen sockets, and noticed the cable drop in the ceiling void.