Not familiar with the UK market, here's a generalization for the AMD line.
Look for at least an Athlon II x3. You can get them stock speed of 3.1 ghz so no overclocking needed for great performance and they are half the price or less than the intel i5 750 generally. If there's extra money, you can look at the Athlon II x4s or Phenom II x3/4.
The mobo should be at least a 760 or higher chipset. Make sure its just an AM3 board needing DDR3 ram and at this point, I'd shoot for one that has USB 3.0 and Sata III. Might have to get into the 8xx chips, but still on budget with the P55.