Hi Nige, you might wanna check out the bulbs in this link http://www.scirocconet.co.uk/forum/new-bulb-trial-t6600.html. Pics on page 21 onwards. Most people on the scirocco forum swear by them, and having seen them in person I would have them, if i didn't already have factory hids. Also the bulbs are e-marked so no problems with the legality side of it. But you will have to email him and see if he has 9006 bulbs.
You also have the piaa white intense option http://www.amazon.co.uk/PIAA-10926-9006-Intense-White/dp/B000MG630I/ref=sr_1_16?ie=UTF8&qid=1382749842&sr=8-16&keywords=piaa+white or the extreme http://www.amazon.co.uk/PIAA-19616-HB4-9006-Xtreme-115-Watt/dp/B0002MAILC which are even better. Very good, but pricey, although a lot cheaper than retrofitting Hids.
All of these options will keep you on the safe side on the law too, and pass mots!
Regards, Sam.