Double pole ceramic fuses with asebestos board separator.
Probably from the 1920s or 1930s.
The remains of the original supply cable can be seen at the bottom edge - cable has 2 copper cores with a lead outer covering.
Double pole fusing has not been permitted since 1955.
After installing the cable, the whole of the lower section was filled with pitch, which is why the original cable has been left in there and just cut off at the base.
Two wall mounting holes can be seen on the back, with brass fixings for the fuseholeders and the lower front cover.
Wiring to the electricity meter and customer's equipment would have been connected at the top terminals, with the round ceramic piece ensuring the wires did not short against the metal case. (One ceramic piece is missing on the left fuse).
Made from ceramic with brass contacts, both are rated 250V, 30A.
A single screw or sealing wire would have held the lid closed.
A chart is printed on both sides of the lid interior, with sizes of fuse wire for 15, 20, 25 and 30A.
In this video, the JP cast iron cutout is dismantled and examined.