The legal element is that some bits of domestic electrical work are notifiable, to find out what is and is not go to the planning portal and download Approved Document P. In order to notify work to building control you can -
A Join a scam eg NICEIC, NAPIT, Elecsa etc
B Pay an exorbitant fee to LABC every time you want to notify a job.
There is an option C but that's being very naughty and will get you a stern telling off if ever anyone can be bothered to do it which is unlikely. Also, option C won't score you any brownie points with most of the guys on here who (rightly) do it by the book and could actually get you tarred with the cowboy brush in your area if it were ever to come out.
Obviously, option A is the way forward. How to join a scam has been done to death on here and continues to be, check out the various organisation's web sites for info on what they want from you in order to sign you up.
Hope that helps.