My friend is renovating an old house in the UK. I was interested to notice that all of the (removed) mains sockets had these plastic terminals on the ends of the wiring coming out of the wall. I've never seen these before - I would have expected bare wires, to attach to screw terminals on the socket fixtures.
I understand that the wiring is pre-2004 standard, with red live and black neutral.
What are these plastic connectors for? Are they intended to plug in to some particular design of socket fixture? To fit to a normal screw terminal socket, would these just be removed?