Verified answer

Best option is ebay.

With that price range, the most you're likely to find are going be laptops that are old, used and probably damaged. You can try searching for laptops within that price on eBay. but bidding can easily go up to over £70. Another option would be http://www.ukstudentlaptops.com/ . I've never bought anything from there, but they do specialize in cheap laptops. I checked the categories for laptops under £99 but there doesn't seem to be any for sale at the moment. You might also want to check your local Craigslist or classifieds to see if anyone wants to get rid of their older computers.