This particular call out was a bit of a lucky find - namely because this socket was the closest to the fuse board where we were carrying out our initial checks. A simple case of human nature leading to a quick find.

From just opening the socket, the slight smell you get from these sorts of high current Live to earth faults was present, but it wasn't immediately obvious what was happening. In fact we thought the buildup of dust inside the socket pattress may have been causing it. It was only a little later we had realised what had been happening - the insulation on the live core had been nipped, likely from being pressed against the metal earth bar on the back of the double socket (as you can see where the black mark is on the back of the socket in the photo). 

It had clearly been sitting there a while, and likely with the extra presses against the socket as things were being plugged and unplugged, had caused the bare copper to get closer and closer to the earth bar.

Insulation reinstated, socket back to wall, all testing fine, job done!