Whatever you do with the conductors in that position you can't cover them with a splashback as there would be no indication of the cable run.
Can you lift a board above and either pull the cables upwards or cut them and joint them under the board? You would have to employ a method of jointing which doesn't require screwed connections (not accessible for inspection) so it's use of a compression tool (ratchet crimper) or soldering.
If the socket is between two others then the cable route between is obvious, if the splash back could be removed for future access then you can simply terminate the cables together with choc blocks and fit a blank face plate.
If the face plate profile fouls the splash back your have to use a metal one such as
If the cable is going to be in a safe zone after the installation of the splashback and the socket is on a ring final circuit or an intermediate point on a radial then the cable ends could be crimped together and heatshrink sleeved, and sheathed by some method (extra large heatshrink sleeve??) and then plaster/fill the back box and install yr splashback.
Would be a far from ideal situation though and you'd want those (ratchet) crimped connections to be totally solid and tested for continuity and IR.
If it's a spur from a ring or the last/only point on a radial then you want to be removing the entire cable run back to the point it spurs from/CU.
Even if the cable is going to be in a safe zone you really want it to be between two other outlets so there is a good indication of the cable run.
If the cables run vertically from the socket then he has to access from above and joint.
Per above. If its a spur then the cable can be disconnected from its point of origin and left in place as it will be 'dead'.
If capping is in place then yes, easy to remove. If not then I doubt anybody would chase the wall out just to remove a cable.
I think that's what TTC is getting at.
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