[emeritus]

While the practice of having different power and lighting tariffs was widespread, it was not universal. The Victorian flat I grew up in still had its original pre-war lighting installation with only the one meter. While there was electric lighting in nearly every room, the only sockets were one 15A in the kitchen and one 5A in the living room. I understand that electrification had been carried out by the old West Ham council at the time when electricity undertakings were the responsibility of local authorities, and that they did it for free. Our neighbour had obviously declined as their flat only had gas lighting until the elderly tenant died circa 1960. It should be recalled that prior to the introduction of the ring main, every wall socket normally had to have its own cable back to its own fuse at the main switch board.

AFAIK the only exceptions were that you could have three 5A sockets from a single 15A fuse if you used 15A cable throughout. Also, unlimited 2A sockets could be connected to the lighting circuit as they were treated as lighting points. The only ones of our relatives who didn't use those 2 way switched BC adapters were an Uncle and Aunt who lived in a post-war pre-fab, because they had at least one 3 pin 5A socket in every room.

So in the days when few people used anything electrical, unless you had enough money to spend on having proper wall sockets installed, plugging into the light socket made economic sense, and in the days when different gauges of proprietary sockets still abounded (2 pin and 3 pin BS546, Wandsworth, Wylex, D&S as well as the current 13A being examples of those I used to come across in various relatives' and friends' houses within a 5 mile radius in the 1950's), the BC adapter provided standardisation. .