Intel Core i5-2400 (not overclockable, but only 10% slower at stock speed than the ever popular -5-2500k)
An ASUS or Gigabyte z68 motherboard. Just pick the model that best fits the budget and the features you want/need. All are good from low to high end.
8gb(2x4gb) DDR3 1333 ram from Corsair, Crucial, Kingston, or Gskill. You do not need the fancy heatsink type either. The plain "unclad" style will work just as well. You will need 64 bit Windows for this amount as well.
The hard drive will be whatever you can get due to the shortage, but a Western Digital 500gb SATA III 6gb/s would be a good choice.
Video card - The Nvidia 560 Ti or AMD 6950 is an all around good choice these days. They are basically equivalent. Here is a handy tool to see how the 560 Ti will perform in various games. You can extrapolate over to the AMD card. http://www.geforce.com/Optimize
Case - These are more of a personal preference, but any good mid to full tower with good airflow and at least one 120mm intake fan, and one 120mm rear or top exhaust fan is preferable. One popular type right now is the Coolermaster Haf series. Some only come with one fan, but extras are only 10 pounds or so.
A DVD RW can be had just about anywhere. I am partial to Samsung.
I would check Amazon UK and Novatech as the best price options.
There are plenty of guides all over the internet. Youtube videos on "build a computer" are very helpful.
The tricky part comes if the thing does not start when all assembled. If you use good components, this is a less likely scenario, but still possible. I have been building for 24 years, and even on my most recent build I got a finicky video card slot on a quality ASUS board. First trouble I've had in many years. It just happens sometimes. It took three re-seatings of the card to get it corrected. No big deal. It has been flawless ever since.
We are always here at the forum to help, and Tom's even has some good guides to get you started.