If Bridgend labc are as dis interested as most of the Valley councils,the chances are they will have little to no interest in your rewiring, unless you bring it to their attention in the first place
Vast amounts of people are in your situation,most are unaware that they have indeed broken the law
Part p is a very vague, if not unknown building reg, as far as most of the general public are concerned
Where a problem may arise if you keep mum about the work,is the future sale of the house, with increasing numbers of solicitors and insurance companies asking for certification and part p notification
In those cases,generally a Pir is used as a remedy before the sale of the house goes ahead
The councils do operate a regularisation process in cases such as yours,but that may be expensive, and may cause upheaval in the worst cases, with some pedantic council official throwing his weight around because of your mistake
If the certification is for your piece of mind only,I would suggest a Pir by a competent person ( not all electricians are fully competent for doing so by the way)
It would be best to make sure that the person you employ, is in fact ,well qualified and experienced,you dont want to compound your mistakes
Leave the labc in ignorance of the rewiring,because as I have stated,here in Wales it seems to be much much less of importance than in England