A white plug with ROCK logo.
This example has '5A' written on in black marker pen, the lid has the Rock logo and the word FUSED.
A section is broken away at the top - typically a small hole would be there to allow inspection of the earth wire.
The flex grip is a flat bar, and one of the screws has ripped out of the material making it impossible to secure the flex.
A single brass screw secures the lid.
Pins are unsleeved brass, and are of the style which easily fall out when the lid is removed.