I was more talking about the fact that the OP seems to have installed a CU and a bunch of final circuits, and is wanting an electrician to come along, connect, test, and say he did the lot.
I realise that. However, as I've just said, even if that were the case (but see below), I really don't see a problem. If, as we've been told, all the cabling is visible and inspectable, the new electrician can effectively approve the design and construction of 'the lot', and test 'the lot' - just as would have been the case if, say, the work had been undertaken by an apprentice under his/her supervision. I would certainly not see any deviation from the spirit, and probably not even the word, of the certification process if this were the case.
However, recent posts from the OP suggest that it may not even be true that "a CU and a bunch of final circuits have been installed". It now sounds to me as if the situation may well even be that a CU and backboxes have been screwed to walls, and (visible) cables run between them, but with nothing yet actually 'connected' (i.e. a classic 'first fix').
As I said, it sounds as if the only real possible issue relates to the underground cable, and I suspect that even a (sensible) BCO would not get too excited about that. By analogy, if a house had an old, now unused (disconnected at both ends) cable which used to feed, say, a cooker or shower, I would think that (provided the cable tested OK) electricians would usually be happy to install a new circuit using that cable, without digging it all out to satisfy themselves about its routing.
Kind Regards, John