as asked what are you after just the 'tower'(case, motherboard, CPU, etc) or do you need a monitor etc. operating system? Also do you(your friend) have an old sata harddisk you can use? The prices are crazy at the moment, you could get a 1gb for £40 now a 160g is almost double.
basic spec tower only, do you plan on adding a second graphics card(sli) in the future(buy 1 570/580 now then add a second 570/580 in the future, you can't slain 570 with a 580 has to be 2 570 or 2 580).
i2500k £168
mb msi z68a-g65 g3 £150 (cashback offer if you buy by 21st November making it £125 once you get the cheaque)
ram Kingston hyperx genesis grey 8gb pc3-12800 1600mhz £40 not worth getting faster than 1600mhz ones
CPU cooler gelid tranquilo £26 cheap/cheerful and allows you to oc CPU to 4.6ghz
Psu corsair enthusiast series tx850m 850w modular £114 don't cheap out by getting £20/£30 psu unless you like fireworks in your pc, if you don't plan on adding a second graphics card(sli) in future can get the tx650m 650w one instead
ssd 128gb crucial m4 £155 256gb version is double
dvdrw £15-£20 pick one tho pioner retail version(comes with Nero burning software) £19 down from £21
graphics card msi 570 £260 msi 580 twin forzer is £90 more at £350
case silverstone raven 3 £110
no hdd or os, comes in at little over £1k before you add delivery(if you go for the 580 and 256gb ssd you're looking at an extra ~£250).
msi cashback offer details
http://forums.overclockers.co.uk/showthread.php?t=18338613