I built my computer a good 3 or 4 years ago and it was on a budget. Made it a gaming computer at the time with an R9 270x graphics card. Now, it's a browsing computer. I don't need the power. Ended up spending 750 dollars. In your terms, that'd be 600 pounds. Still gets the job done today.
Let me know how much you spent and what you needed it for!