Yes they do come from above. But I intended to replace the cable like for like but install in oval conduit. I fear the excisting cable might be damaged as it's embedded in plaster. But I'll have a look. But I have a feeling I might have to leave this one now. As it falls under noitifiable work.
why should the cables be damaged by being embedded in plaster? an IR test will soon confirm if they are OK. in your place i would just dig out 6" above sockets and fit new sockets. is RCD protection in place?