Get a nice basic $40-50 1155 motherboard (MSI makes some good quality cheap stuff), and then get one of the Ivy Bridge i3 processors when they are released at the beginning of September.
Get 4-8GB of 1333 or 1600 ram
Onboard graphics should be enough for the games listed, but if you find that it cannot keep up then you ought to be able to get by with a $50 GPU... just make sure your power supply is large enough for whatever GPU you choose.
Mobo: MSI H61 or B75 $40-60
like this:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130639
or this:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130654
CPU: i3 3xxx processor (due out 1st or 2nd week in Sep I believe), $90-120
-try to get a model number that ends in a 5 (ex: i3 3xx5) as they will have better onboard graphics, and will be more likely to do what you need.
Ram: 4GB in a 2x2GB kit or 8GB in a 2x4GB kit, $20 or $40
Sorry, I don't quite know how those prices translate into pounds, but it would be within the budget and do what you want.