In terms of BS7671-compliance, it is not for me to decide where the 'tipping point' is or to 'have a logical, consistent set of criteria that have to be met'
Of course it is and of course you have to.
As soon as you decide that you don't have to comply with BS 7671 editions/amendments when they come into force, but may wait until some point in the future, you absolutely must have a definition of your tipping point and you absolutely must have a set of criteria which make sense to you (even if nobody else). If you don't then your approach is without logic and without rigour, and therefore invalid - you cannot have regulations based on emotion.
- but 'sensible' regulations might be expected to.
I'd be interested to see a suggestion from you for changed wording of, say, the last sentence of 522.6.202, to provide a codified method, which could be consistently applied by everybody, to incorporate your concepts of "only a few feet of new cabling", or "x% of the existing wiring not complying already".
As things stand, BS7671 is clear, in requiring any new work to comply with current regs, even if the vast majority of the installation doesn't. What is far from clear, and open to much debate and interpretation, is whether adding, say, and extra 5% of work which is non-compliant with current regs (but which should be compliant) to an installation in which 100% of pre-existing work was non-compliant (in the same way) with current regs (and doesn't need to be compliant) is sufficiently 'unreasonable' (in terms of safety) to constitute non-compliance with Part P. In the sort of cases I'm talking about, one could certainly have a good stab at arguing that it wasn't.
This sort of thing seems to be a habit with you.
You decide that regulations do not mean what they say, or
you decide that they don't have to be followed, and then
you decide to embark on a process which you hope will result in an "interpretation" which corresponds to your decisions, and then you find that ambiguities and inconsistencies etc arise. When will the penny drop that
you are the one responsible for those problems, not the people who wrote the regulations which
you decided should not be followed?
As above, what is required to achieve BS7671 compliance is clear - the issue is what constitutes "reasonable provision ..." in order to achieve compliance with Part P.
Indeed, that is not prescribed.
But once the decision to use BS 7671 compliance as the "reasonable provision" then you can't have some vague, emotional non-rules of "it's only a few feet of cable", or "it's only one additional socket".