Good service
John Surtees The cheapest I could find was at <http://nativedigital.co.uk/shop/>. With free next day delivery. Also on their site is a free downloadable 66 page colour guide.
After some initial problems, I e-mailed for advice and got a reply in under half an hour from Rob Griffith, who is, I believe, one of the co-founders of the company. After sending a screen shot of the calibration problem, Rob suggested that I might have activated the Universal Access contrast control by mistake. Apparently this is easily done by mistake, as the keyboard shortcut is one used in other applications, including Photoshop. Sure enough that was it.
Excellent service from the cheapest supplier. As Rob said in his reply to me, after commenting on this: 'There's no reason why low price should mean poor service'. How refreshing!