Very heavy old unit in thick bakelite housing.

Almost double insulated, but not the switch.

Red wire is active, 240 jolts.

I've never heard of the brand: any idea of where it was made?  GUESSING that the voltage means that it was for European use - right?

https://www.itri.co.uk/index.php?option=com_mtree&task=viewlink&link_id=29944&Itemid=11

I think this could be the answer but I can't open it further.

I tried too. The post is dated 2001 and may have timed out or is no longer supported. It does give a reference to Ironmonger's Weekly 1948 P 944  issue? 1851.  Maybe you can find that in an archive somewhere.  I'm betting that some other articles might be interesting.

I Googled "Ironmonger's Weekly 1948" (including quotation marks) and got two links to something called ITRI - "Delivering the Future of Tin" - but it appears to be a sort of member's-only site, and I didn't go through the effort of trying to get in and find the item.  If you try this, highlight the green address beneath the blue header; click "Open in new tab" or "open in new window", and you'll get there.  Registration is at https://www.itri.co.uk/ .