It’s in the wiring regs, not building regs if that’s what you’re asking, I can’t quote you the specific reg if that’s what you were hoping for. I remember being quoted chapter and verse when I wanted to link my business and residential properties that were only meters apart, the sparky I had on staff who was normally quite tame was having non of it. It didn’t happen for other reasons, but my recollection was the earthing of two buildings is different and isolated, when you link them, that’s bad. He also didn’t like the suggestion of armoured cable without sheath isolation (read a gap and heat shrink).
You’re right about not knowing op’s skill set, we do know that you have no awareness of PoE injectors, and it seems reasonable that if someone can plug a powerline adapter in and run a cable to it, they can probably plug a passive PoE injector in and run a cable to a P2P adapter of whatever type. As it doesn’t fall under electrical minor works, it doesn’t need an electrician to issue a minor works cert, so literally anyone ‘competent’ can do the job. If doing it as part of a business they would need PL covering cables carrying low voltage, but that’s literally about as exciting as it gets in a domestic setting, so this is largely unskilled territory and it’s a few minutes work at each end. It may even be easier if you have a horse as it saves getting the ladders out and the Stetson could stop dust getting in your eyes
