On Mon, 11 Mar 2019 14:41:24 +0000, Roger Hayter wrote:

For anyone who thinks wiring is too easy to be left to the
professionals. In our bathroom the fan permanent live is supplied from
the socket circuit (admittedly from a fused switch unit next to the
sccket in the cupboard under the sink) and the switched live is from the
lighting circuit. I don't suppose this is totally forbidden,


Yes, it is totally forbidden!
521.8.2 says L +N of each final circuit shall be electrically separate
from those of every other final circuit.

There will be more, but ICBA to look them up now.

Suffice to say, it can be dangerous how yours is, and should be rectified
to make it safer, i.e, get the permanant live from the same circuit as
the switched live.