When we moved in 3 years ago, in the lounge there was a surface-mounted plastic pattress on the wall backing on to the kitchen. It was right in the corner with the lounge external wall, and about a metre off the floor. On it was a paper label stating "circuit is disconnected". Within a couple of hours it got lost behind the TV, and I forgot all about it.
Until this weekend, when I had to get behind the TV, and saw it again. I wondered what was behind what appeared to be just a label over a blanking plate, so unscrewed the cover. I expected to find only bare wires, or maybe covered with insulating tape, which would be par for this place. What I found was the mains cable going into a standard brown plastic block of the sort you'd find in any socket, switch, fused spur, etc, But I could see nothing on the front. It seemed completely flat; there was certainly no switch. And the label wasn't big enough to have covered a 13A socket. I pressed the label a bit harder, and detected some indentations. It then became clear what it was - an old round 3-pin socket for lighting. At this stage I decided to put a test screwdriver on the screw holding the red wire. Of course, it was live! So much for it being disconnected...
Then I noticed that there were two cables attached to the block. One appeared to go to the outside wall, and then the penny dropped. In the lounge there are three picture lights, all on different walls. One light was on the outside wall, about a couple of metres from this 3-pin lighting socket. On the outside of the house behind the light there was some trunking, which went from the light to what I thought was the kitchen. I could just see a cable re-entering there. I couldn't see it on the inside, and had assumed it was just below the work surface and hidden behind something. Now I know it goes to the 3-pin socket.
It's probably a good time to get rid of all this junk as we never use the picture lights (all of them are different styles - again par for this place). Two of the lights are up against the picture rail; the other one is about 25 cm below it. The latter and the one on the outside wall (and the 3-pin socket), are controlled by the wall switch. The light nearest the wall switch isn't controlled by it. It's on its own circuit and is controlled by a switch on the light fitting! I think I'll fit a central light to complement the standard lamps we already have. There will be some plastering and painting required, but hopefully not too much.
By the way, does anyone know when these 3-pin lighting sockets stopped being fitted? This place was built in 1965 and has one, as did out previous place built in 1978, but not the one before that built in 1982.