I'd advise getting a pc built around AMD components. they seem to do worse performance-wise than intel/nvidia in the higher echelons but do offer a value for money which beats Intel/nvidia on the non-gaming and budget setup hands down..
Ask the kind people of http://www.reddit.com/r/buildapc, I was looking to buy a new pc about a month ago, and I registered on reddit after my housemate advised me to ask there, and within an hour I had a few people giving me advice which ended up affecting which particular components I purchased, in a positive way.
I'd advise to get a 4gig of ram (leaving you with about £270), but can't really advise on particular models as I don't know much about which AMD product would be optimal for this sort of thing.
Look for a second hand i5 bundle on ebay, I would not buy AMD unless you only intend on playing old games which might be the case ESP if you're talking about built in graphics.
Now I will get myself the GeForce GTX 650Ti for something like 130-150€. If we count that together we get something between 480 and 500 Euro, which converted to £ is something like 408 to 425. But if you go with AMD you probably will save like 40%.