Anytime,
I would have a look around for these bits, its a vague spec; it will be helpful to do a bit of reading on the products; reviews mainly. i will help you were i can.
The Vague Spec:
i5 2500k (CPU) ~£170
a Z68 Chipset ~£90-£110 (gigabyte do a good one)
GPU; GTX560ti ~ £170 or 6950 2GB ~ £200
Power Supply; 550W - 650W PSU ~£40 - £60
22" LED Monitor ~ £160 (dell do a good model i think).
Case; (this is personal choice) Some good models are Antec 300, Cm 690II and Bitfenix Shinobi. ~ £40 - £60
8GB RAM; DDR3 1600Mhz ~ £40
HDD's (price have gone a bit mad recently, just have a look around) Anything that has a enough space will do you fine for now.
If you are going to be Overclocking in the future you will need an after marker CPU cooler. The Corsair A50 is a good one ~ £25
Optical drive ~£15
Total (minus HDD) ~ £840
The Z68 chipset and the (k) series processor allows overclockability in the future. as will the after market cooler. A 6950 or GTX 560ti will run any modern game on high settings. The i5 2500K is the best price/performance CPU on the market at the moment.
Have a gander, I hope this helps.