To be fair to the OP this is a rather unusual situation.
My opinion based on what we know-
FI? Well the only thing we don't know is where it connects, and OP has done his best to determine there are no accessories downstream of the joint.
C1? No one is one single action away from danger
C2? As it's left the cable can't be used by an ordinary person, so hard to say that it's potentially dangerous.
C3? We'd definitely recommend improvement. Ideally if redecoration ever permits it the joint would be found and dealt with.
I think I'd C3 it.
(I might stick an FCU with 5A fuse on the end of it with a 5A Max label, then I'd feel that I'd done all I can to prevent anyone overloading the cable in future. )