Tesco- Used Laptop sold as new?

So last week I bought a Sony Vaio from Tesco- I paid �449 for it (the new price) however when I got it home I knew instantly something was wrong. Firstly although the Tesco staff had cleverly put their own security seal over the rim of the box the one Sony put there had clearly been broken. The Laptop seemed to be packaged as new but again, upon powering it on there was more evidence that I was not the first person to use the laptop- the User account was registered to some guy called Ali, the hard disc was full of pictures of him and his family and now I am not only finding it difficult to change the details of the Laptop from this Ali guy but am also worried about how long he was using it for, what malware the Laptop may have been exposed to etc. My question is; are Tesco allowed to sell a clearly used Laptop as new? It's not a discontinued line nor did I get any discount compared to the 'as new' price- I want a new Laptop because that's what I paid for- not a second hand one. Where do I stand as far as my statuary rights are concerned?