I understand that it is not acceptable to run the wiring for a spur horizontally from one socket to another, plus this is a dry wall and beams make this not possible anyway.
Is it acceptable to run the cabling vertically up from the existing socket into the loft above, across in the loft and back down the wall in the position of the new socket?
Yes if all the requirements are met. Horizontal is also permitted. However any spur must either be fed with a fused connection unit (FCU) or be only spur from a point on a ring.
In theory if two cables go to a socket then you can spur off it. However that assumes the socket is installed as per regulations in first place. In real terms many rings are broken and many people have also spurred from a spur.
Your problem is do you have the skill to test what you have to know if in your case it is permitted?
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