http://www.transportoffice.gov.uk/crt/doitonline/bl/mottestingmanualsandguides/mottestingmanualsandguides.htm(EDIT: new link)
Section 1.7 on HIDs
Nothing mentioned in fail section for aftermarket systems.
Information - 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; however, it is accepted that it may not be possible to readily determine the functioning of self levelling systems. In such cases, the benefit of the doubt must be given.
Headlamp washers may work in conjunction with the windscreen washers (when the dipped beam headlamps are switched on) or by a separate switch.
HID lamps may be identified by:
taking a few seconds to reach full intensity
having a bluish tinge to the light
having an igniter module/inverter behind the headlamp
having ¡¥DCR¡¦ marked on the headlamp lens.
HID headlamps use high voltage and extra care should be taken when inspecting these items.
method of inspection
Where HID or LED dipped beam headlamps are fitted, switch on the headlamps and check the operation of any headlamp levelling and cleaning devices fitted.
Reason for rejection
A headlamp levelling or cleaning device inoperative or otherwise obviously defective.
JJ