I am an electrician I've just never worked for myself and domestic isnt my bag at all. I've always worked for companies. I can test and inspect. I know what the readings are and what the readings have to be. I can inspect and test. I just dont know the ins and outs of certification
To get a completion or compliance certificate if required when your not a scheme member means telling whoever is going to do it before the work starts, they tell you at what stage they want to inspect, and in Wales where I live it costs £100 plus vat, so in the main if it needs notifying simply not worth doing DIY.
They with me at least did not want to inspect themselves, but wanted to use a local electrician which would have also have paid for by me. So cost of inspection can easy be over the cost of whole job, so in real terms unless a rather big job under the £2000 limit but getting close to it, or LABC charges are waved, or it does not need notifying then not worth doing as DIY.
If a rented house no option, but owner occupied who will find out? The only time anyone is likely to find out is if some thing goes wrong, which one would hope as an electrician nothing will go wrong, however having minor works or installation certificates does show you took due care, and lists what you have done, rather than some one before you. As to what needs notifying that is a little grey where we are told using a FCU does not form a new circuit so clearly not using BS7671 definitions so it is down to the courts to decide, and it will only go to court if you get it wrong.
So a consumer unit is a type tested distribution unit, so unless all inside the CU is type tested to be used with the CU then it is not a CU, I don't think this argument would stand up in court, but it would need to go to court, which will only happen if you get it wrong.
Domestic is not my bag either, but I can read, what the problem is difference in law and approved document, and what case law has been established. And it seems where things have gone wrong, there is far more than simple Part P in question. But as to running a new neutral it is so easy to fit wireless switches just can't see the point.