Not sure on changes with 18th Edition, but with 17th Edition it would have been OK to wire in Ali-tube cable and use RCD sockets.
It adds around £12 to socket price, but it is the Al-tube cable that I found the problem, as a retired spark I can go to local supplier and buy 5 meters of twin and earth, but if I want ali-tube it's a drum or nothing.
So in the main whole job costs same as changing a consumer unit, so is a non starter.
So the only real way is the RCD FCU and use all fused spurs for extra sockets.
Of course the BS7671 is not law, so as a retired electrician I can add sockets as long as not a kitchen, or outside (I live in Wales) without needing to tell the LABC there is no law to stop me. However most electricians who work on domestic sign paperwork with their scheme provider to say they will follow BS7671, so they are breaking the law if they don't follow BS7671 unless their scheme provider says they can, and of course since a safety matter this must be in writing, an email or text is OK, but not a phone call.
Yes I know until 2004 we had very few RCD's and it was not until 2008 that we really started to fit them, and I see why one would think done without for a centenary why do we need them now?
What my answer is "people now expect them" so people are not as careful, and as an electrician we must look at if it all goes wrong, what then. There was a court case over the death of Emma Shaw, to me an eye opener, the foreman got a prison sentence, the electricians mate who was one of four tradesmen who made errors, got away with it. And no amount of insurance will cover a prison sentence, so simply not worth doing anything which will remove your ability to earn money.
I had mothers house rewired because she saw a red flicker on an extension lead (it was the neon) thought it was no fire and put it in a bucket of water. Yes she had dementia and eye sight problems. But so may your little old lady in 5 years time. Just not worth the risk, know it sounds like sucking through teeth and jobs worth, but it is exactly that, not worth risking your job to do it, after all she can use extension leads.