The use of the word "Mandatory" could often be taken, by many people, to mean a legal requirement. ... The wiring Regs are not a statutory document and therefore do not have the force of law *...
As I hope you realise, that is the (and the only) reason why I responded to Murdo's use of the word 'mandatory'.
As you go on to say, there is, in England, a legal requirement for compliance with BS7671:2018 for private rented properties, with a legal requirement that defects with EICR codes of C1 or C2 be remedied. However, at least in theory, even that does not inevitably mean that an installation without 'required' RCD protection would 'fail' the EICR (hence requiring 'remedial action') - since the one (and only) instance of BS7671 giving any guidance on EICR coding is where it says that the absence of required RCD protection should be given "at least a C3".
Having said that, we've been told nothing about rental and the OP seemed to imply that we're talking about owner-occupied premises.
RCDs are pretty much mandatory to comply with the wiring regs. ......... Therefore not mandatory in law but an extremely good idea to comply and perhaps foolhardy not to!
I don't think any of us would argue with that - but that does not alter the fact that RCDs are not, strictly speaking, 'mandatory'.
If required by contract between parties then the wiring regs might apply.
True, but if it's an owner-occupied house, I don't think that there will be any contracts - and, even if there were, it would be a 'civil matter'.
If there is an electrical disaster and subsequent injuries to persons, livestock or property the you mighthave to explain to a bloke in a wig, whilst you are gripping the bar, why you did not comply with the wiring regs or ask to explain how your actions provide similar alternative protection (such as the wiring regs of another civilised country) or alternative suitable means.
That is all true - but, being pedantic again (through a desire to avoid anyone being 'misled') again, does not mean that RCDs are "mandatory".
Having said that, I have to wonder how often instances of "an electrical disaster and subsequent injuries to persons, livestock or property" which were arguably due to non-compliance with BS7671 have got anywhere near a court!
Kind Regards, John