Here's what I recommend :
PCPartPicker part list:
http://uk.pcpartpicker.com/p/3gPLz
Price breakdown by merchant: http://uk.pcpartpicker.com/p/3gPLz/by_merchant/
Benchmarks: http://uk.pcpartpicker.com/p/3gPLz/benchmarks/
CPU: AMD Athlon X4 760K 3.8GHz Quad-Core Processor (£58.05 @ Ebuyer)
Motherboard: MSI A88XM-E35 Micro ATX FM2+ Motherboard (£40.15 @ Amazon UK)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-2133 Memory (£55.36 @ Ebuyer)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£35.99 @ Aria PC)
Video Card: Gigabyte Radeon R7 260X 1GB Video Card (£91.19 @ CCL Computers)
Case: Corsair 200R ATX Mid Tower Case (£45.90 @ Amazon UK)
Power Supply: XFX 450W 80+ Bronze Certified ATX Power Supply (£20.00 @ Maplin Electronics)
Total: £346.64
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-03-26 17:28 GMT+0000)