It's known as a Wylex plug and they came in two types: ring main (13A) and non-ring main (15A). Looks like that's a "non" one (without a fuse). I think there were probably other manufacturers of the design, but that seems to be a genuine Wylex one. They're a collectors item, though not that rare - so don't throw it away.
It would be interesting to know which local builder/electrician fitted them. The BUDC had a thing about those terrible fused pin ones which frequently fell to bits. Everybody was surely glad to see the back of those! They became ridiculously expensive, and the fused pins hard to get hold of, which brought on their rapid demise in the late 1960's. The Wylex design probably failed in the 1950's, or maybe just post-war.