pages 3,4,9,10 and 12 of approved document P
The approved document is not Statutory Law, just a guide to help you comply with the law. The building regulations on the other hand are the law. This is what is actually written in The Building Regulations and what is on the statute books,
"PART P ELECTRICAL SAFETY
Design and installation
P1. Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installation from fire or injury."
I just hate the way you electricians quote regulations and documents, half the time not related to the particular installation being discussed, and make it out that you are quoting law and scaring people into thinking they are breaking the law and acting unlawfully, when in fact you know very well that approved documents and wiring regulations are not law and purely guidelines.
I believe my cable is safe as it is protected by an RCD. If an unprotected cable run under plaster less than 50mm in a wall is considered safe, because it has RCD protection, then I say a cable run in a ceiling, less than 50mm under plaster is equally as safe.