Im pretty sure hid conversion isnt illegal as yet, most likely fail an mot which in itself is illegal, but anyhoo.
Im all for HID conversions, i do it to every single one of my cars, cant say ive lost any value in them because of it either. I believe they are much safer at night, as you can see more without dazzling other drivers, but please remember if you do them yourself, make sure to check your headlight levels to make sure you wont blind oncomming vehicles, as most of the time when people whom have done the hid conversions, dont bother just checking and thats generally why they dazzle you . My two cents.
