[David G4EBT]

I think they actually originated not simply as a means of convenience to plug into a light bulb socket, where there weren't enough power sockets, but as a bit of a doge because there were two tariffs with some Electricity Boards - one for power, one for light. As a kid in the 40s and 50s, they abounded everywhere, sometimes with a 'Y' socket and a switch, so that the light bulb could stay in place, and whatever was plugged into the socket could be switched on and off.

As Dave Moll says, bayonet (and E.S.) sockets are probably the least safe items around the home.

I have a neighbour who lives alone and tries to be independent. She'd had a light bulb which went off with a bang and the glassware of the bulb fell onto the floor. She asked if I could help because try as she might, she couldn't get the brass bayonet fitting out of the light socket. When I went to have a look at it, the RCD at the Consumer Unit hadn't tripped and the light switch was still on. She told me she'd been "trying to 'unscrew' the brass bit but couldn't manage it as she didn't think her grip was strong enough". She'd been using a pair of uninsulated pliers, a few millimeters away from the live contact in the socket, attempting to 'unscrew' the remnants of the brass bayonet part of the dud bulb. Without her good luck and good fortune, it could have had a tragic outcome.