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[UK] Found during house renovation
(i.imgur.com)
There is a key to lock it closed, and the same key will lock it either on or off. In keeping with a Victorian Bell/Butler Board but not near it in the house.
I guess it must be some kind of isolator switch, but I know nothing of its history.
Guessing by the size of the wires this was meant to switch Mains power and was set u to cut/connect both legs at the same time. Since you mentioned a butler call board, it could have been used like this.