That’s what I suggested earlier see post #11).!! I don’t try and help just to be ignored.Just a thought could I use one of these?
https://www.screwfix.com/p/appleby-2-gang-47mm-dry-lining-box/45057
Called a few electrical wholesalers in Leicester and they don't have them.
So, my last bit of help;-
But 47mm is way too deep, you’ll need to chew a couple of inches off the vertical stud. go for the usual depth one (32mm). Available everywhere. Screwfix, b&q, Jewsons, everywhere
good luck