Fits a variety of outlets
The bayonet socket allows a lamp to be plugged in directly - or less helpfully, a bayonet plug or another adaptor.
Note the socket has a basic shutter mechanism, concealing the live pins unless significant pressure is applied to the round plate inside the socket.
At the widest setting, the unsleeved pins are very close to the edge of the adaptor.
There is no makers name, but the end is marked 'ER2' and 'MADE IN ENGLAND'.