I believe it is an MOT fail to place LEDs into Halogen headlights.
I think this is an example of where the legislation is failing to keep up with technical developments. Sure, it's a bad idea to let people put any old LED bulb into a reflector/lens setup designed for H4 bulbs, but now that you can get LEDS that replicate the light spread of H4, I can't see an issue. I had no problem getting the Landy through its last MOT with a set of H4 LEDs installed.
