Not mine, but nasty little bit of wiring
Doing a few things at my daughter's place including just 'replacing some light shades'. But when I went to remove the shade the fitting simply dropped down (held by a tiny end bit of one screw) to expose this delight (see pic).
A DIYer who knew enough to get into trouble and not enough to get out. Had used a bit of 3-core flex to extend a light fitting and had connected Blue (Neutral) to Active (Red) and Brown (Active) to Neutral (Black). But that's alright, he realised the wall switch wasn't doing what he wanted so he re-wired that too . . .
Ah well, it's worked for many years, but through luck and his ignorance getting the single circuit working (he swapped the colours behind the wall plate - so was switching active, but using the black wire up to the fitting as the active!).
Sigh . . .
Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.