Hows this,Slightly over budget at £332.02 but i think thats the best your going to get for the money and to be able to play games smoothly.
AMD Athlon II X4 640 Socket AM3 3GHz 2MB L2 Cache Retail Boxed Processor
http://www.ebuyer.com/product/242140
MSI 880GM-E41 880G Socket AM3 onboard graphics 8 channel HD audio mATX Motherboard
http://www.ebuyer.com/product/244433
Kingston 4GB (2x2GB) DDR3 1600MHz HyperX Blu Memory Kit CL9 1.65V Non-ECC Unbuffered
http://www.ebuyer.com/product/234975
Gigabyte GTX 550 Ti OC 1GB GDDR5 Dual DVI Mini HDMI PCI-E Graphics Card
http://www.ebuyer.com/product/260567
Samsung SH-S223 22x DVD±RW DL SATA Optical Drive - Retail Box Black with Software
http://www.ebuyer.com/product/179014
Corsair 600W CX PSU - 2x PCI-E 6x SATA
http://www.ebuyer.com/product/241000
Coolermaster Elite 330 Black Mid Tower Case
http://www.ebuyer.com/product/127584