Brown bakelite adaptor with a 5A plug and three 5A sockets.
The socket in line with the plug is a three pin BS546 type, as is the plug.
The two side sockets are two pin BS372 types. The space where the third earth pin would be is actually used for screws which hold the adaptor together.
Although similar, the hole spacing for the two and three pin sockets is different, so a two pin 5A plug will NOT fit into the holes of a three pin 5A socket.