since I don't do domestic I can't vouch for certain, but if it's a refit, then it goes where the old one was.
If it's a new build, then it goes at low level close to where the meter box outside is i suppose.. to cut down on lenght of mains tails..
unless it's a block of flats situation then it goes next to wherever the mains cables enter the flat ( asuming that the meters would be downstairs under the stairs etc ) or where the DNO cable and meters go..
if its a new build it has to comply with part m.thats why its at the height its at.no other reason.everything has to be in that 450mm to 1200mm zone including the cu.just imagine yourself sitting in your wheelchair in the dark,wishing you could reach the cu if its at high level!