All very interesting and informative
Now, rules is rules, so it's interesting that the DFT's article is a statement of their interpretation of current law, not drafting/proposing new legislation. I guess the key point is the requirement for auto-leveling and washer devices.
However, I've just looked at the 2012 MOT inspection manual which require that these functions operate where fitted, not that they are fitted in the first place. Rejection only if "a headlamp levelling or cleaning device is inoperative". If beam spread and everything else is ok, there doesn't seem a reason to fail a car with aftermarket HIDs.
So, aftermarket HID kits are illegal, but you won't fail your MOT. Seems a little inconsistent, right?
I'm sure this has been discussed at length here somewhere, but just my ha'pennies worth!