See revised MOT rule effective from 11th January 2021.
4. Lamps, reflectors and electrical equipment
4.1.4 Headlamps - Compliance with requirements - Changed sentence from 'Existing halogen headlamp units should not be converted to be used with HID bulbs. If such a conversion has been done, you must fail the headlamp.' to 'Existing halogen headlamp units should not be converted to be used with high intensity discharge (HID) or light emitting diode (LED) bulbs. If such a conversion has be