Rob, do you happen to still have that specimin? It looks VERY similar to the sockets in my new house, some of which are showing slight, faint scorch marks on the fronts (I will be changing them shortly). These sockets, when the switches are on, you can rub off the "on" text with your finger. Unsure what brand.
No I'm afraid it's long gone. It was maybe 3 years ago, and I can't remember what brand it was.
It was a tumble dryer wot did it!