Build me a gaming pc for £400-500

http://www.tomshardware.com/forum/274745-31-step-step-g...

Sites to buy parts
http://www.scan.co.uk
https://www.aria.co.uk/

Suggested build (no OS or Monitor, those will be extra)

system bundle
http://www.scan.co.uk/value-hardware-bundles
VB15i

LN27738 4GB (2x2GB) Corsair DDR3 XMS3 Classic, PC3-10666 (1333), Non-ECC Unbuffered, CAS 9-9-9-24, 1.50V
LN43271 Gigabyte GA-H61MA-D2V Gen 3, Intel H61, 1155, DDR3, SATA II 3Gb/s, PCIe 3.0 (x16), D-Sub/DVI-D, Micro ATX
LN42826 Intel Core i5 3450,1155, Ivy Bridge, Quad Core, 3.1GHz, 5 GT/s DMI, 650MHz GPU, 6MB Smart Cache, 31x Ratio, 77W, Retail
LN3096 NO HEAT SINK AND FAN
LN41164 Scan Value Bundle Range
LN41167 Scan Value Bundle VB15i Intel
£191.19 £229.43

LN43569 1GB Sapphire Radeon HD 7770 OC, 5000MHz GDDR5, 28nm, GPU 1150MHz, 640 Cores, Dual Link DVI-I/ HDMI/ 2x mini
http://www.scan.co.uk/products/1gb-sapphire-radeon-hd-7...
£91.77 £110.12

LN40852 NZXT Source 210 Elite Black Mid Tower Gaming Case with USB 3.0 w/o PSU
http://www.scan.co.uk/products/nzxt-source-210-elite-bl...
£29.98 £35.98

LN35692 500W PSU, Corsair Builder Series CMPSU-500CXV2UK, 80% Eff', Uncertified, Quiet Fan, ATX v2.3
http://www.scan.co.uk/products/500w-psu-corsair-builder...
£37.39 £44.87

LN42410 1TB Seagate ST1000DM003 Barracuda 7200.14 SATA 6Gb/s 7200rpm 64mb Cache 8ms NCQ OEM
http://www.scan.co.uk/products/1tb-seagate-st1000dm003-...
£57.10 £68.52
-----------------
Total£499.11

For BF3 if you really want to turn up the eye candy, I'd try to get a little bit more in the budget for a stronger video card than a 7770, yea it will do the trick, but if you can get some more umph from something like a 7850 or a GTX 570, or even an older GTX 480 I would do so. Other than that, Jerred's build gives you a real nice running start.

Don't forget OCUK
http://www.overclockers.co.uk/