This is about the best you can get for that money :
PCPartPicker part list:
http://uk.pcpartpicker.com/p/1yx0Z
Price breakdown by merchant: http://uk.pcpartpicker.com/p/1yx0Z/by_merchant/
Benchmarks: http://uk.pcpartpicker.com/p/1yx0Z/benchmarks/
CPU: AMD Athlon II X4 750K 3.4GHz Quad-Core Processor (£58.50 @ Scan.co.uk)
Motherboard: MSI FM2-A55M-E33 Micro ATX FM2 Motherboard (£35.46 @ Scan.co.uk)
Memory: Corsair XMS3 4GB (2 x 2GB) DDR3-1600 Memory (£24.13 @ Amazon UK)
Storage: Seagate Barracuda 500GB 3.5" 7200RPM Internal Hard Drive (£35.99 @ Aria PC)
Video Card: MSI Radeon HD 7770 GHz Edition 1GB Video Card (£77.72 @ Scan.co.uk)
Case: NZXT Source 210 Elite (Black) ATX Mid Tower Case (£38.65 @ Scan.co.uk)
Power Supply: XFX 450W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply (£34.99 @ Maplin Electronics)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer (£12.86 @ Amazon UK)
Operating System: Microsoft Windows 8 (OEM) (64-bit) (£69.66 @ CCL Computers)
Total: £387.96
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-09-01 03:11 BST+0100)