Just for fun I built an i5 Computer out of your budget. It was originally for you, but... I went 60 Euros over the limit. I'm posting anyways because I spent quite a bit of time and tried to work with what I got, so why let that effort go to waste?

Enjoy.

Case: http://www.ebuyer.com/product/143854 ~~~~£39.73

Motherboard: http://www.ebuyer.com/product/173450 ~~~~£136.84

CPU/Processor: http://www.ebuyer.com/product/172755 ~~~~£144.31

RAM/Memory: http://www.ebuyer.com/product/180490 ~~~~£79.99

GPU/Graphics Card: http://www.ebuyer.com/product/176938 ~~~~£116.98

PSU/Power Supply: http://www.ebuyer.com/product/127861 ~~~~ £49.98

HDD/Hard Drive: http://www.ebuyer.com/product/150246 ~~~~£42.29

Subtotal: £610.12