Grelco 5 Amp double adaptor
One 5A plug to two 5A sockets.
These allow two 5A plugs to be connected to a single 5A socket.
These adaptors are unfused.
Both sockets are identical, BS546 5A, three round pins.
The underside is marked with the Grelco logo, 'Made in England' and 'Max Total Load 5 Amps'.