I've had the 6000K kit on mine for 3 years now - passed 2 MOTs and failed 1 with them fitted (I swapped the bulbs for the originals and it passed, so I'll just swap them prior to MOT

)
Anyway, if they are aftermarket fitted then yes they are deemed as illegal but think you would be very unlucky to be pulled for them on the road.
Loads of info about them on here, search under HIDs