£156.89 CPU Intel i5 3570K Quad 3.4Ghz
£46.30 CPU Cooler Thermalright HR-02 Macho and Thermal Paste
£51.55 Motherboard Asus P8B75-M LE Micro ATX
£43.86 RAM Patriot Limited Ed 8GB (2 x 4GB) DDR3-1600
£67.27 Hard Drive Seagate Barracuda 2TB 7200RPM 3.5"
£98.79 Graphics Card Radeon HD 6950 2GB
£45.55 Case and PSU CiT Orion with 500W PSU
£29.99 SSD OCZ Vertex Plus 60GB SATA-300 2.5"
£540.20 Total Ebay could be cheaper
The 6950 is an aging card. Just be aware that crossfiring it/etc will not be possible when they completely disappear in about a month. If its really cheap then I would say go for it still -- but if its the same price as newer cards the newer card is the better bet.
I'm not sure about that Orion PSU (dont know much about them). Can you provide a link to the case and PSU?
I wouldn't get that PSU, it only has 300W on the 12V rails (the reliable ones have almost all of their power on theses as they are the rails you'll use most) and is probably built to the minimum specifications and so lacking many of the safety circuits i's take for granted.