Latest handbook issued 1st Jan

http://www.dft.gov.uk/vosa/repositor...n%20Manual.pdf

HID requirements

"Vehicles equipped with High Intensity Discharge (HID) or LED dipped beam headlamps may be fitted with headlamp washers and a suspension or headlamp self levelling system.
Where such systems are fitted, they must work;"

So nothing about not being able to retro fit them or type approval, only that if washers etc are fitted they have to work