Brown bakelite adaptor used to connect three plugs to a single socket outlet.
Both pins are the same size, so a plug can be inserted either way round. Not suitable for appliances requiring an earth connection.
This adaptor is not fused, so it would be easy to overload the socket - theoretically 15A from a single 5A outlet.
The back states Made In England, and a small circle contains the rating - 5A, 250V.Stuff