I have some pretty early BS546 plugs that did have sleeved pins - a red sleeve on the live and black on the neutral. I think they were made by GEC sometime in the 1940s or 1950s, I also have a Crabtree one with sleeving too, from around the same time. Obviously they were ahead of their time and didn't catch on, possibly due to the small extra cost. I'll see if I can get some pictures and have them posted.
