Quote Originally Posted by BobB View Post
I know LEDs need a lot of bulky electronics
Barely bigger than a standard bulb (they have a small heatsink on the back). You are thinking of HID which requires ballast and relays.

MOT regs tightened up last year, retrofit HID is now an automatic fail and I'm not sure of the status of retrofit LED (Though I believe either without a specifically designed reflector/housing is against C&U so an offence).