I used stuffing glands, as to new circuit, it seems a little vague as to what is considered new, so if I want a socket local to consumer unit, and I fit it to the existing ring final overload, then not a new circuit, it is an extension to an existing, and if I then decide I want it on it's own overload, and move it across it again is not new, clearly there should be a minor works raised for both jobs, giving the paperwork trail, and clearly circuits which are altered should be inspected and tested, but the new circuit may tell the electrician when a compliance certificate is required, but for owner/occupier it means nothing.
Clearly with rented property you need the paperwork, be it minor works, installation, or EICR, the paper trail is very important, but with owner/occupied who would know if paperwork not raised. Clearly it needs inspecting and testing, before it is energised, but as to paying the LABC for a completion certificate, it may be legally required, but only time I did it correct, they never even visited the house, it just came through the post, and when I tried to get a replacement they said it would take 4 months, if they can find it, and charge depends on how much time they spend finding it, in other words the whole completion certificate is no more than a tax.