Try
www.dell.co.uk/outlet (there are other non-UK versions)
These are returned laptops which are then rebuilt and properly tested but then sold as second-hand. I used to be a bit dubious as to why they were returned but found out that the vast majority are returns by shops such as Tesco who ordered 100,000 but only sold 70,000.
If you're wondering how I found out - I used to work for them.