I reckon those 2.5mms need fusing down at the point where the CSA decreases. C3.
Are you saying one end of the ring is fed by the 32A MCB, the other would be fed by the 20A breaker if it didn't appear to be broken? I reckon a bit of further investigation could be required there.
I don't see that the socket needs coding. Yes it's rough, the sort of thing a DIYer would do, but in a commercial property it's not likely to be used by anyone with restricted reach.
The MCBs on those lighting circuits need changing. C2.
If it's what I'm thinking of those Gewiss boards are horrible to wire - they're basically just a plastic box. Do you have a picture of it?