You didn't mention for what is he going to use it ?
CPU: AMD FX-8320 3.5GHz 8-Core Processor (£109.98 @ Amazon UK)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (£23.98 @ Scan.co.uk)
Motherboard: ASRock 990FX Extreme3 ATX AM3+/AM3 Motherboard (£74.70 @ Amazon UK)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory (£59.99 @ Scan.co.uk)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Disk (£69.99 @ Amazon UK)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£41.40 @ Aria PC)
Video Card: Sapphire Radeon R9 270X 2GB Video Card (£148.45 @ CCL Computers)
Case: Corsair 300R ATX Mid Tower Case (£58.98 @ CCL Computers)
Power Supply: SeaSonic S12II 620W 80+ Bronze Certified ATX Power Supply (£67.11 @ Amazon UK)
Total: £654.58
(You can swap CPU with FX-8350, price will still be under £700(£687.07)).
or
CPU: AMD FX-8320 3.5GHz 8-Core Processor (£109.98 @ Amazon UK)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (£23.98 @ Scan.co.uk)
Motherboard: ASRock 990FX Extreme3 ATX AM3+/AM3 Motherboard (£74.70 @ Amazon UK)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory (£59.99 @ Scan.co.uk)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Disk (£69.99 @ Amazon UK)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£41.40 @ Aria PC)
Video Card: Gigabyte Radeon R9 280X 3GB Video Card (£227.05 @ Dabs)
Case: Corsair 300R ATX Mid Tower Case (£58.98 @ CCL Computers)
Power Supply: SeaSonic S12II 620W 80+ Bronze Certified ATX Power Supply (£67.11 @ Amazon UK)
Total: £733.18
Yep, I'm AMD's fan so I went with AMD CPU.
Or incase you want to go with Intel solution:
CPU: Intel Core i5-4670K 3.4GHz Quad-Core Processor (£156.94 @ Amazon UK)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (£23.98 @ Scan.co.uk)
Motherboard: ASRock Z87 Extreme3 ATX LGA1150 Motherboard (£84.99 @ Ebuyer)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory (£59.99 @ Scan.co.uk)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Disk (£69.99 @ Amazon UK)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£41.40 @ Aria PC)
Video Card: Sapphire Radeon R9 270X 2GB Video Card (£148.45 @ CCL Computers)
Case: Corsair 300R ATX Mid Tower Case (£58.98 @ CCL Computers)
Power Supply: SeaSonic S12II 620W 80+ Bronze Certified ATX Power Supply (£67.11 @ Amazon UK)
Total: £711.83
Water cooling ?
CPU: AMD FX-8320 3.5GHz 8-Core Processor (£109.98 @ Amazon UK)
CPU Cooler: Corsair H80i 77.0 CFM Liquid CPU Cooler (£75.00 @ Amazon UK)
Motherboard: ASRock 990FX Extreme3 ATX AM3+/AM3 Motherboard (£74.70 @ Amazon UK)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory (£59.99 @ Scan.co.uk)
Storage: Samsung 840 EVO 120GB 2.5" Solid State Disk (£69.99 @ Amazon UK)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£41.40 @ Aria PC)
Video Card: Sapphire Radeon R9 270X 2GB Video Card (£148.45 @ CCL Computers)
Case: Corsair 300R ATX Mid Tower Case (£58.98 @ CCL Computers)
Power Supply: SeaSonic S12II 620W 80+ Bronze Certified ATX Power Supply (£67.11 @ Amazon UK)
Total: £705.60