As of 20th May 2018.
HID bulb fitted to a Halogen headlamp unit with result in MOT refusal :!:
See here for more new MOT rules coming into force as of May 2018. They include more tighter rules for DPF's & EGR's etc.
viewtopic.php?f=5&t=184386.
If you wish to use HID then you should replace halogen headlamp unit for a HID headlamp unit