[rogerdraig]

is the fire working ?

if it is i would not do this

1 if you are going to reduce the thickness of wall to inset tv there could implications varying from structural integrity to heat damage to wall and tv
so consult a builder and tv manufacturer ( not just about warranty but whether it could be a fire risk )

2 ridding the wires will be very hard

if its not working

then your best option is to get a builder to take the from wall out completely and put in a lintle it will be less work and less time than chisseling out an alcove

with the wall gone you can put a stud one in in place with alchove in it

then all you need do is drill a 50mm hole through th brast side that hace the equipment you are attaching to in it o feed the wires through from inside the fire place