Well, considering the fact that you live in UK, which means you're a VAT payer, and that means prices are 20% high than in USA, this is the best deal I could find:http://www.amazon.co.uk/Samsung-550P5C-15-6-inch-Laptop/dp/tech-data/B007VBEQ56/ref=de_a_smtd
I know it's over your budget, but that's the minimum I'd go as far as gaming go.
Gaming wise, it's as fast as 350-400 pound desktop would be.
It will play games like Far Cry 3 or Hitman Absolution on medium settings at 1366x768 resolution. Games like MW3 should be playable on high settings.