"Borrowed neutrals present a significant danger to anyone working on the circuits affected, it has never been permitted in the regulations as far as I know." Always puzzles me this one, to who exactly does it pose a danger? This situation with borrowed neutrals is viewed as though it is an isolated incident that should be treated as some kind of potential disaster that should be sorted out as a matter of urgency. It is not a C2. There are hundreds of thousands of houses that have borrowed neutrals on the hall/landing lights, that's how they were installed years ago, to save £££'s. To fix most of them would entail large scale work and probably significant re-decorating, which in a lot of instances is impractical. I have come across dozens of these situations in dwellings that have had them for donkey's years and they have never resulted in injury or death as far as I am aware, any "electrician" who is working on lighting circuits (of any description) should be aware that they are possibly the greatest source of danger in a domestic environment and act accordingly, and anyone else should not be working on them at all. Its another case or real world verses red specs world.