Closer to the top end of your budget:
2011 model Lenovo G series Lenovo G570 £380
Core i3-2310M 2.1GHz Sandy Bridge CPU, 4GB RAM, 320GB HDD, 15.6" 1366x768 LCD w/ HD 3000 graphics.
2010 model HP G72 £370
Core i3-350M 2.26 CPU, 3GB RAM, 320GB HDD, 17.3" 1600x900 LCD w/ Intel HD graphics