For that budget, have a look at Ebuyer. They have a number of laptops on discount offers.
I recently purchased a Fujitsu Siemens Esprimo V5535. Got the laptop, carry case, extra 1GB of ram, 2x double mouse kits, free next day delivery, all for £307.83 and that included 7 days of free technical help (if needed).
On that purchase, I was a little concerned about certain things, and the telephone sales team provided all the answers, including that I had just missed out on the free 1GB ram upgrade, which then cost me another £15.00 into the above final price.