10A socket and matching plug with a a round earth pin. It can specifically be used for controlled circuits, usually in commercial buildings. Manufacturer: HPM (part of Legrand group)

Hi, its a special use socket that was commonly used on storage heaters especially in commercial/gov buildings.

Cyril

Seems to be a special purpose one or for a dedicated circuit. Sometimes found with old nightstore heaters?

Its done that way so only things with the correct plugtop can be plugged in, dedicated supply outlet.

Saves some guy plugging in his toaster at the hospital ad tripping the circuit that has equipment keeping people alive on it, things like that.

yeah, just a round earth pin socket. many manufacturers make them - for all the reasons above