Thanks all for the replies.
One that I can go to and remove the parts myself would be good to know about (preferably in London, Bristol or Shropshire), but one that is happy to post could also be useful. I need the starter as soon as possible, so either will do for now; I'd prefer to be able to save the cash and remove them myself in general though.
This one is the best I know.
http://www.iberkshire.co.uk/profile/61986/Wokingham/A1-Wokingham-Car-Spares/
Always plenty of cars. A good turnover of models and the guys that work there are fantastic (and MB fans)
Many cars are stacked and you have to ask the forklift guys to get them down for you.
Once done you can help yourself.