My Roadster S1 is now equipped with LED in wing ligths and pilot lights in the headlamps. As far as I know, there is no MOT issues with that. It had absolutely no negative effect on the mains or dip beams. There are also LEDs in all tail/stop ligth, license plate, reversing and fog tail light. No problems, and with the low current draw, I guess the hydraulic brake switch hopefully will last forever. There will be no H4 LEDs in the headlamps, for MOT reasons. I fitted relays to the mains/dips, resulted in considerably light output.