i'll have fingers crossed for you that there is only 1 wire in the socket cos getting the floor upstairs is about the only proper option that or put a hole in the cieling with a big hole cutter find the 2 cables going behind the plaster down the wall cut them in the ceiling and use a plastic junction box to connect the 2 wires back together again to complete the ring then get the piece of plaster board that come out with the cutter put a piece of wood above the hole screw it through the ceiling so it solid then screw the cut out piece back where the hole is and then a little bit of filler and a lick of paint to cover it all up, it'll be the least hassle way of removing the socket completely you can just cut the cables out the socket box and fill it in and leave the cables behind the plaster.

i'm presuming it's plastered walls and boarded cielings, not lath and plaster, or plaster board walls