hiding tv cables, UK?

well its a solution most installers have used. but if its an outside wall with a ton of plumbing or stuff in the way it can be a pain in the ***. interior can also be a pain in the butt but its usually a little easier. id just cut a small hole behind your tv mount and stick a stiff wire or coat hanger down until you find either the bottom of the wall space or an obstacle. that way at least if their is an obstacle you wont have any visible holes to patch. we use an inspection camera but we do it enough that it was worth the money. although i should note that the power cord shouldnt be ran down inside the wall. you would need to use an inwall rated power cable like the powerbridge or have an outlet installed behind the tv.

Your discription seems to fit with the DIY recommendations and the clean appearance of wall mounted flat screens placed by professional businesses. Links two and three show a visible cord cover kit option and an in-wall option.

http://www.allbcd.com/wp-content/uploads/tvart.jpg

https://www.legrand.us/wiremold/tv-cord-cover-kit....

http://www.legrand.us/wiremold/at-home/cord-organi...

http://www.cepro.com/article/recessed_power_low_vo...

http://www.powerbridgesolution.com/powerbridgeprod...

done all the time --- a two or three inch hole will repair easier if necessary and just a foot off the floor is all you need ==== an oblong cut is easier with an old steak knife ,,,,,

depends how old your house is and how wall is constructed ..if fairly modern the wall could well be full of soundproof insulation ....and if constructed properly there will be noggins built in ..horizontal bracing ...I always fit noggins ...this will prevent your idea ....either way your 4" hole is way too big