I have installed hybrid but reading BS7671:2008 likely it did not comply, as current rating of cable changed, it was a massive warehouse, refrigerated which needed cleaning so they wanted sockets for the cleaners, the distance from distribution board was well over the then limit of 80 meters now 102 meters for volt drop, so we used 10 mm² in a ring of SWA in the loft space going into boxes above where each socket was required, then a spur to the sockets down the wall.
10 mm² x 2 would not have gone into the sockets, and each drop was around 20 foot down the wall, so this method ensured a good loop impedance and minimal volt drop, it did the job safely and neatly, however as said not sure if it strictly complied.
Seen the same with large houses, really pointless having two 2.5 mm² cables running together with no sockets until end of run, and volt drop for 2 x 2.5 mm² far higher than with 16 mm² and since 16 mm² will not fit in a socket it clearly needs a junction box to go from 16 to 2 x 2.5 mm² it makes sense, however the problem is where some one comes latter and says oh 16 mm² I can use a 45A MCB for that. In theory you should run the 16 mm² to a mini consumer unit then to ring final.
What we want is a FCU which can take a 32A fuse, however as far as I am aware they don't exist? Same with hob and oven, don't really want a 45A MCB protecting the 2.5 mm² cable going from the duel cooker connection unit to the oven, it needs a 16A fuse, it would not be that hard to make a fused duel cooker connection unit with a 32 and 16 amp fuse inside, however for domestic it needs type testing so until some manufacturer makes them, we can't use them.
