If you don't have any luck at halfords, you could try:
http://www.bikecolours.com/index.html
http://www.paints4u.com/AboutP4u.aspx
http://www.motorbikepaint.co.uk/
not used them myself, but they might be able to help perhaps.
I tried GSPD750's method and bought a couple of touch up sticks from what the local car place had in stock which looked right in the shop but were way out when I tried them, so like he say,s make sure you match it up outside in the sun if you try that.
I think you can probably get the base white colour code easy enough from the sticker under your seat though (or wherever they are on the rd07s) without needing to have that colour matched.