It is a problem to put in cables
There's a choice - you can either
1) Run a cable from your upstairs study into the loft, buying the trunking, making a hole in the ceiling. Then across the loft to another room where the cable can go down. Hole in the ceiling again.
More trunking, then either use a specialist hole cutter to cut a hole in the huge floor grade chipboard, or dig up the nails with a screwdriver and an industrial strength tack remover or a hammer, cut hole, replace.
Another hole in the ceiling of the room below. Lots more trunking, eventually reaching your endpoint.. When happy, paint over trunking to disguise it.
Time : hours. Expense : not inconsiderable. Effort : lots. Nice, fast and interference free though.
(or a hole to outside, piping, another hole to inside the house. Buying a very large drill, fitting piping or external grade CAT5 to wall, in through the house again with more trunking)
2) Stick in a wireless access point. Find it conflicts with the other 10 wireless access points, drops out and provides shit speeds.
Time : minutes. Expense : low. Effort : minimal, but it may not actually work
3) Spend fifty quid. Put one homeplug device in one socket. One in the other. Run short cable from each one. Job done.
Time : Seconds. Expense : 35-60 quid. Effort : none. Speed and reliability : high
Now replace the above scenario with cabling to another room.. More trunking, more holes, more effort. Homeplug? Unplug, move to other room, plug back in.
I've got a very small amount of sympathy for the fact some homeplug devices interfere with shortwave, but pretending that 'it's usually not a problem' to install cabling is complete and utter lunacy.