I have found this on a website
Are these Xenon HID systems road legal?
According to EU legislation HID systems standard factory fitted from the factory require a self levelling system and a lens washer to be fitted. However this is not specified for aftermarket kits. Our kits have passed all safety and emmissions tests and produce the correct light pattern. We know they will pass an MOT (original bulbs can be reinstalled in minutes if required without uninstalling the HID system). We are not aware of any legality issues over the use of aftermarket HID kits when installed correctly and when the colour tempature is 6000k to 8000k but it should be worth noting that car headlights have to produce a white light so the 10000k and 12000k kits may be a bit blue / purple for legal road use.