If you really want to reach the ceiling of your budget:
CPU: Intel i7-930 2.8GHZ LGA1366 £240
http://www.ebuyer.com/product/193596
Mobo: Asus P6X58D-E X58 £180
http://www.ebuyer.com/product/219007
RAM: Crucial 6GB (3x2GB) DDR3 1333MHz/PC3-10600 Ballistix Memory CL7 1.65V £126
http://www.ebuyer.com/product/159927
GPU: Sapphire HD 5870 1GB GDDR5 £320 £320 x2 = £640
http://www.ebuyer.com/product/199644
Or
XFX HD 5970 Black Edition 2GB DDR5 £540
http://www.ebuyer.com/product/179863
Just one 5970.
PSU:Corsair CMPSU-750W HX Modular PSU £120
http://www.ebuyer.com/product/164950
Powerful enough for two 5870s and an OC on the CPU.
SSD: Intel X25-V 40GB £88
http://www.ebuyer.com/product/190701
For a boot/OS drive, maybe one or two games. You can drop this if you don't mind waiting for your OS to load up, or want to wait for the technology to mature.
HDD: Samsung HD103SJ Spinpoint F3 1TB OEM £55
http://www.ebuyer.com/product/173804
OR
Seagate ST31000528AS Barracuda 7200.12 1TB OEM £55
http://www.ebuyer.com/product/158798
For storage and other apps/games that won't fit on the SSD, or perfectly fine as an OS/boot drive.
Case: Coolermaster HAF 922 £81
http://www.ebuyer.com/product/164961
OS: Windows 7 64bit Home Premium OEM £78
http://www.ebuyer.com/product/173791
If you want to OC the CPU:
Some thermal paste:
Arctic Silver 5 £6
A
Prolimatech Megahalems £43 and a
Scythe S-Flex fan, £13.
£1671 (most expensive items with aftermarket heatsink). Which probably doesn't leave you the ideal amount to get a really nice monitor, so you could take the 5970, a single 5870 or maybe a 480 if you not mind the heat, noise and power consumption of one (or two for which you'd need an 850W PSU) of those.
I do not know monitors well enough to give a definitive recommendation, but I think you should look at 22-24", 1680x1050 - 1920x1200 res. Try to find one with high contrast ratio (dynamic contrast is not the most reliable spec or sometimes even give good performance), low response time 2-5ms.
You could save some money by changing the CPU, mobo and RAM to the following.
Intel Core i5 750 2.66GHz Socket LGA1156 £168
http://www.ebuyer.com/product/172755
ASUS P7P55D-E PRO £170
http://www.ebuyer.com/product/194854
G-Skill 4GB (2x2GB) DDR3 1600MHz/PC3-12800 Ripjaw Memory Kit CL7(7-8-7-24) 1.65V £102
http://www.ebuyer.com/product/180490
Which would save £106, which would be plenty to get all the other peripherals you need. The i5-750 would perform very similiarly to an i7-930 in gaming so might as well go for the i5. And 4GB is plenty for most gaming.