I know you said you want an AMD build but heres a good idea if you can consider Intel.
Intel Core i5-2500k - £159.59
4GB Mushkin Blackline - £25.85
Seagate Barracuda 500GB - £30.24
Gigabyte GA-Z68A-D3 - £77.56
XFX ATI Radeon HD 6850 - £124.99
450W XFX Core Edition - £34.80
Xigmatek Asgard - £28.99
DVD Burner - £13.93
Total - £495.95 Before Shipping.
Doesn't have the cooler but youre not going to need to overclock for a while anyway.