Building control seem to do what they like, I fitted a wet room for my late mother, and although the regulations say with an opening window you don't need an extractor fan, the LABC inspector insisted one was fitted.
If a room is used for a new function it seems LABC are often involved, living room turned into a kitchen, kitchen turned into utility room, and as an electrician we are often unaware of when the LABC is involved, so unless told we want sockets at x inches above floor level, the safe option is to fit as if a new build.
I can see the reason for placing sockets above the axle height of a wheel chair, their largest wheels normally same as push bike, so 311 mm from floor, below this hight a wheel chair user can easy smash a socket as often they don't see back of their wheels when turning, I noted throughout the ground floor in my mothers house, the damage to walls up to 320 mm, so sockets at 350 mm means in the main out of harms way.
As to making sockets so can be used by wheel chair users, they are sitting down, so as long as not in a corner and above skirting height not a problem, the problem is when mounting items too high not too low. Wheel chair users eye hight around 1200 mm, if the item needs viewing from above, then needs to be under that hight.
I don't think the person writing the regulations has ever used a wheel chair, or been in the home of a wheel chair user, there was no problem upstairs in my mothers house, she simply could not get upstairs, why have an area not accessible with a wheel chair wheel chair friendly? Sockets at the bed head need to be where the bed will not damage them, so not between 250 mm and 600 mm needs to be lower or higher.
Even specialist disabled kitchen installers get it wrong, using a touch control hob which the controls not visible at the angle viewed in a wheel chair, or oven controls with the numbers printed on the top, so a disabled person can't see the temperature set.
