Exactly, and that's why I believe that the author of the regulation deliberately 'singled out' G/Y singles for prohibition of over-sleeving, believing that the practice was acceptable (and not 'bad workmanship') with G/Y-insulated cores of multi-core cables.
That doesn't mean that I'm very comfortable with the practice, but I could understand the reasoning.
As I wrote to BAS, failing to understand that a blue conductor over-sleeved with brown is being used as a line conductor (i.e. thinking it is a 'neutral') is, in practice, very often going to be just as disastrous as failing to understand that a G/Y conductor over-sleeved with brown is being used as a line conductor (i.e. thinking it is a CPC) - yet BAS seems to regard the former as OK, but the latter as unacceptably poor workmanship.
Kind Regards, John
Getting a live wire mixed up is very different from a earth to live wire. Remember neutral is considered as live. I have never considered it acceptable to use the same colour for a phase as neutral however for years blue was both a phase colour with fixed installation and neutral with portable, it is like swapping from driving on left to driving on right and having the wagons do it this year and cars next year.
We have the same with black, for years is was neutral, now it's a phase colour.
We have swapped phase and neutral colours for so long now, no one can really complain. Earth was originally green, however red/green colour blindness is common so it was changed to green/yellow.
I can understand where some fixed inaccessible wiring, say the supply to wall thermostat, is found to need a neutral after the thermostat is changed, so some one uses the earth wire as a neutral and over sleeves it. I don't think it's right, but can understand it, and if in the future some one connects it to earth, then it may trip the RCD, but unlikely to do much else.
However I have seen one meter lengths of flex from a junction box to a cylinder thermostat which could be changed to 4 core in minutes, and some one has used the earth wire as a line.
When I wanted to fit a third light switch in my mothers room I needed 4 cores, since one core with most 4 core is coloured green/yellow I bought 5 core, it was actually the same price, so why does anyone with an original installation over sleeve the earth wire?
It asked for who designed, who installed and who inspected and tested, and clearly if you need to use the earth wire there is something wrong with the design.