Without opening up a can of worms (and this is the only post on this subject I will make as I'm sick of it frankly
)
For Type approval you are supposed to have Washers and Auto Leveling or self-adjutsing rear suspension.
There are some cars that came FROM THE FACTORY (mainly Japanese Imports) which were not subject to this.
For the sake of the MOT the BEAM PATTERN needs to be correct. You could have nuclear power stations for headlights technically so long as they had the correct cut off and beam pattern.
Officially if your headlights are under 2000 lumens you don't need washers or levelers, if they are over 2000 lumens you do, however there is no accurate way of testing the lumens in a garage, so they apply the "lowest common denominator" which is simply the beam pattern - In short you can fit a HID kit as so long as the cut off is correct (which it will be in the Hella housings or quality aftermarket Projector units, they will NOT be in the factory reflector headlights) your vehicle will pass an MOT.
I have this in writing from VOSA directly.