It used to be I don't know if it is still the case that if alterations by their nature changed the Standard in such a way that you must produce a new edition. What that such a way was I couldn't tell you.
Probably in BS0 the Standard to which other Standards must adhere to.
Your TT becomes a separate system with your earth fault loop path using the electrode. It no longer relies on the main installation earth so that is not part of your TT Zs.
The "loop" doesn't play a part in the circuit switching as such. With switches it is normally used for the neutrals which are now commonly connected through switches for future smart options.
Been watching this for years although I skipped most of Sylvester McCoy.
Watched the Christmas episode but seeing him in a skirt I thought nope no more.
I agree a box ticking exercise and shan't even have a gander.
Probably wasting your time. The chances of it being free from conductive parts of the electrical installation is probably zero especially if the steelwork is the main structure as opposed to a small "floating" part.
It is a functional switch therefore it should be capable of that function. Small gentle tap with a smallish hammer normally resolves it then remove the flaked paint.
5.18 of the Inspection Schedule, Condition of accessories............. is relevant.