Part P (in fact all of the Building Regulations)
applies to any work whatsoever on fixed electrical cables or fixed electrical equipment located on the consumer’s side of the electricity supply meter which operate at low or extra-low voltage and are—
(a) in or attached to a dwelling;
(b) in the common parts of a building serving one or more dwellings, but excluding power supplies to lifts;
(c) in a building that receives its electricity from a source located within or shared with a dwelling; or
(d) in a garden or in or on land associated with a building where the electricity is from a source located within or shared with a dwelling.
Not all work is notifiable, and if you read
Schedule 2B you'll see what is and what isn't.
This job isn't, but you are legally obliged to comply with Part P:
P1 Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.
If you have the knowledge and skills etc to do it safely then you may do it.