Tim is correct on the legal issues regarding LEDs in the headlights.
I've had LED sidelights fitted at my last two MOTs and H4 main/dip LEDs at my last one without issue. The H4s I fitted are H4 Philips LUXEON ZES, weren't cheap but give a reasonable beam pattern and lots of light. The beam pattern is no worse than standard but there is now adequate lighting for night use. I did have one of them vibrate apart last year and had to screw it back together with the supplied tiny Allen key - they have screws that allow them to be configured for left or right side of the road.
