Being pedantic, "Part P" is irrelevant to the thread - all it says is that electrical works need to be safe.
What IS relevant is the appendix to the Building Regulations that specifies what is or isn't notifiable - from memory it was App 4 in the 2005 BR and App 2 in the 2013 BR. In England only three things are notifiable since 2013 :
- Addition of a new circuit.
- Replacement of a CU.
- Work within the zones of a bathroom.
And that is it. Wales kept the more complicated rules from 2005. Scotland has different rules. Dunno about NI.
If you do do notifiable work, there is tge option of notifying direct to the LABC dept. However, in many cases that will cost more tgan just getting a scam member to do the work. If it's not standalone work, e.g. building an extension, then just include something like "and associated electrical works" in the BR appkucation for the project.
In terms if results, my experience is "don't ask" - just provide a professional looking set of documents and BR are likely to accept them. If you ask, you give them tbe opportunity to impose requirements such as requiring testing to be done by a scam member.
Of course the scams, err schemes, would prefer that people thought more work has to be done by their members. In support of that aim they put out documents etc. with clever wording which is "just" truthful, whike also being deliberately misleading.