Quite an old one, never seen one with terminals like that and the old colours.No idea ... but it's been 'on my shelf' for many years, although I can't recall where it came from or why I happen to have it. However, as you've seen, the L and N connector blocks are coloured red and black, which probably means that it is pre-harmonisation - hence at least 20 years old..
Hang on ... I'll see if it is still there....
... yep, it isIt looks totally unused, but bears very few markings - certainly no indication of the manufacturer. Other than L, N & E markings it has just "Made in England", "PROV PAT" (which I guess probably means "provisional patent"?) and, interestingly for a double socket "13A".
Probably
Thanks.

