Hi C-H
BS 1363 13A sockets have always had safety shutters, it was part of the standard, I think 13A sockets first appeared around 1948.
The older BS 546 sockets are usually found with shutters too, I don't know if this was required by BS, as I've seen some really old installations (1930's)with unshuttered 5 & 15A sockets.
I think the Brits may have been first with safety shutters!
Also British sockets almost always incorperate a switch, so that you do not have to unplug appliances on load.
BS = British Standard.
