I really think that this is all down to common sense, and one would hope that any court that became involved would similarly exercise common sense. Ironically, prior to the 'relaxations' (in England) in notification requirements last year (and still in Wales), the Building Regs made it explicitly clear that adding fused spurs to an existing circuit did not require notification. It seems inconceivable that they intended that the 'relaxations' would result in such previously non-notifiable things becoming notifiable. I would suggest that (i.e. 'IMO') when there is just a single CU/DB, the common sense definition of 'new circuit' (in the context of notification) is probably fairly clear - namely a circuit which originates from the CU/DB and was not previously there (and excluding spurs of pre-existing circuits which happened to originate at the CU). I agree it gets a bit less obvious if one has CUs feeding CUs (as is common with sheds/garages etc.), but that's a bit different.
The need for realism and pragmatism is something I've often discussed, and had very heated debates with BAS (as sometimes others) about. I do understand the viewpoint of PBoD, BAS etc, but if that is one's view, then the only real solution would be close forums like this (and leave DIYers to their own devices), since the only alternative would be (as BAS often did) to answer almost any question with advice not to do it, on the basis that, amongst other things (and as you say), almost no ordinary DIYers would have the facilities, knowledge or inclination to undertake the 'proper required testing'.
I've always acknowledged that there is a dilemma. However, if forums like this are to exist, and if the likes of us are going to make the decision to participate in them, then some sort of 'realism', or whatever you want to call it, has got to be exercised, otherwise the whole thing becomes extremely silly and there is simply no point.
Kind Regards, John
