North Metropolitan Electric Power Supply Company
The top corners have small holes to hang the metal plate on a wall, presumably adjacent to the fusebox.
Northmet was a private electricity company based in Wood Green, London.
The sides of the plate are folded to conceal the sharp cut edges.
The indents for the fusewire are clearly seen from this side, these are partially cut at the top, bottom and sides to form tabs that the fusewire can be wound behind.