It probably won't be relevant to that many people, but I've added the fitting price for Camskill based on what I paid the last time I got a full new set:

Site..........................Price Fitted.......Price Not-Fitted

Blackcircles.com..............£313.68............£265.58
Tyreshopper.co.uk.............£341.20............N/A
Camskill.co.uk................£318.00............£277.04
eba_y_tyre.store (ebay).......N/A................£283.00
Topgearshop (ebay)............N/A................£284.00
Allnewtyres.co.uk.............N/A................£290.16