dont buy them from mini, i had a xenon bulb go before, just swapped the other one over to see if it had blown. it wa just the bulb so went on
HIDS4U Ltd - UK's Number 1 HID Conversion Kit Specialists, they are £68 for both bulbs, its best to change both at the same time, i bought these ones below:
D2R Bulb*::*Replacement HID Bulbs*::*HIDS4U Ltd - UK's Number 1 HID Conversion Kit Specialists
they are brighter than the original, these are 6000k where as the standard ones are only around 3400k, they look so much nicer at night time. and you can see better and are still legal, had mine for over a year now and been great.