I choose 750 PSU so that you can add another R9 270x in future.
I suggest to get FX 8350 if you more money
PCPartPicker part list:
http://uk.pcpartpicker.com/p/3vGJP
Price breakdown by merchant: http://uk.pcpartpicker.com/p/3vGJP/by_merchant/
Benchmarks: http://uk.pcpartpicker.com/p/3vGJP/benchmarks/
CPU: AMD FX-6300 3.5GHz 6-Core Processor (£76.79 @ Aria PC)
Motherboard: Asus M5A97 R2.0 ATX AM3+ Motherboard (£64.76 @ Scan.co.uk)
Memory: Kingston Beast 8GB (2 x 4GB) DDR3-1600 Memory (£53.00 @ Amazon UK)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£42.73 @ Aria PC)
Video Card: Asus Radeon R9 270X 2GB Video Card (£149.99 @ Novatech)
Case: Corsair 200R ATX Mid Tower Case (£45.90 @ Amazon UK)
Power Supply: Corsair Builder 750W 80+ Bronze Certified ATX Power Supply (£63.98 @ Dabs)
Optical Drive: Lite-On iHDS118-04 DVD/CD Drive (£10.78 @ Scan.co.uk)
Total: £507.93
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-04-21 14:28 BST+0100)