These brown plastic boxes are older types, probably from the 1970s. The newer ones are made from cream coloured plastic.
This example was poorly installed. Note the excessive bare copper showing on the incoming tails (top right), the lack of sleeving on the CPCs (earth wires) at the top left, and the massive holes smashed out of the back panel.
This box is rated to 45A maximum, yet has 2x 30A fuses installed. This supplied a cooker circuit, and all of the socket outlets in a kitchen. It is therefore likely that the total load would have exceeeded 45A.
As with most of these fuseboxes, the fuses are the rewireable type. The fuse wire passes through the centre ceramic section and is secured with a screw at each end.
Internally, there is only the frame which the fuses and switch are mounted to. There is no back plate or back box - the wall it was fixed to formed the back of the enclosure. For mounting on combustible surfaces, a separate flat panel was available to fix behind the frame. This was not used in this example, despite the box being fixed to a wooden board.
The internal frame with fuses removed. The incoming connections are top left. Outgoing neutrals bottom left, earth top right above the fuses.