I've followed all the advise, he needs to get someone with more experience. If you fancy a drive to Glasgow?.. I didn't get access to the loft to check for cables damaged or so. I could change the rest of the sockets I didn't change. Or than that.
Take a short break and then go back. you will never gain the skills you need if you don't keep trying!
Taking a systematic and logical approach is essential or you will be chasing your own imagined tail. You might have more than one fault, you might have a fault in a hidden junction box, but if you apply some of the suggested tests you should be able to pin down the two sockets where there is an unacceptably high r1 between them.
At that point you have a couple of courses of action.
You can double-check that the two socket connections are fine, at which point you know there is a "cable" fault. It might be the hidden fault is feeding a spur, so if you isolate both good ends (so sockets 1...A are all good one one leg, and C...N are good on the other leg, but B is now open - its a spur off a junction box).
The locations of them might give you a clue as to what is up.
Maybe the junction feeds something you have not found (e.g. aerial amplifier in loft?)
If you find both isolated legs are moderately similar numbers of sockets and no other problems then you might call it quits and put them on two 20A MCB/RCBOs as radials and be done (after checking the Zs values...)
Imagine the RFC, now think of a section as bad and think "How can I find it by measurement along?"