tern you should look in back of the socket below. bet it's 6mm T/E and was originally a cooker outlet someone has chasnged for a socket. replace socket with 1 of these.
Crabtree 45A Cooker Connection Unit White | Switches & Sockets | Screwfix.com
Crabtree 45A Cooker Connection Unit White | Switches & Sockets | Screwfix.com