Yeah as Gh0sT1321 said, your gonna have to buy an operating system which probably set you back further £70 (Amazon)
Also theres no mention of what make the PSU is, i'd private message him to find that out.
I see it's entitled "fast gaming PC" so I assume you want to use it for gaming, in that case the GPU (graphics card) is the lowest
6000 model out and i very much doubt it'll be able to cope with the newer games out on highest settings so you may want to look into upgrading that. (£80 for a 6750 maybe?)
Overall i'd say it's not a bad rig, with those points in mind - go for it!
That's not a gaming PC. It has a Radeon HD 6450, which is pretty much an HTPC card. Also, you need an OS. Not to mention, it's overclocked, and they don't tell you what model PSU is in it. For that price, I'd put my money on it being an off brand.