Right, here is what I have in mind (all from Amazon.co.uk for simplicity, there are of course many others like Aria, Overclockers, ebuyer, Scan, etc. which will offer better prices).
£156.96
i5 4570 Brain of the rig,
£76.61
Gigabyte H87-HD3 Motherboard, there are plenty to choose from.
£54.99
2x4Gb 1600Mhz Corsair Cheapest 2x4 1600Mhz kit I can find off Amazon.
£189.30
7950 Sapphire Graphics card, if you look around other sellers you should be able to find free games bundled (Crysis 3, Crysis 3 Blood Dragon and Bioshock Infinite)
£84.99
Seagate 1Tb SSHD Good compromise between speed and price, according to users comes near to SSD speeds with HDD prices.
£59.52
Corsair GS600w "Good enough" power supply. Ideally you should go down to 500w, but other than CX Corsairs with dodgy ratings (30C?! I still use them
) this is the next step up
£17.35
LG DVD drive Optical, you can get rid of this if you don't need it. I personally will include for convenience.
£41.99
NZXT Souce 210 Cheap case of the pick
£69.99
Win7 SP1
Total: £751.70
I'll do the optimisation later