how many watts are you consuming already for the 13A socket? Better don't exceed 1500 Watt per socket, or else the plug will heat up if you use it continuously for long hours. Don't know what will happen if it is overheating continuously.

the proper way of adding more wall socket is pull a new line from the existing fuse box that has the least load.

anyway, if your house has 3 phase power, it is possible that you are unable to use broadband over powerline.