Your friend has a black one in Stoke? I have a DMG and apart from when I've been up to Middlehurst I've never seen another GTR on the road yet, lol!
If you check out the detailing world forum there are a couple of detailers based in the Stoke area. Ones that spring to mind are Auto Detox in Litchfield and Prestige Valeting. There is also Mirrorfinish, based in Cheshire, who will also cover the Stoke area.
Check out the DW forum for some examples of their work. I know that AD has posted some work on a Ferrari that they have recently done and Mirrorfinish have detailed a black GTR - pics are on their website.