Be careful of places like PC World and Currys.
Those places tend to sell brands of laptops that are only available from their shops and nowhere else.
Therefore you have no idea of the quality of the product, or what the "real world" cost is, you only know what THEY are selling it for.
I would also guess that the sales people have some sort of incentive to sell those brands, so they are more likely to push those brands to get their "bonus".
Brands I am thinking of are EI System and Advent for example.
Stick to one of the "big boys" who sell their laptops anywhere, such as:
Toshiba, Acer, Sony, Fujitsu Siemens, HP Compaq and so on.
As Ethel says, around �399 seems to be the price point for a "decent" laptop. You can get cheaper but they tend to skimp on build quality, or memory or disk size.
Try and top it up to �399 and you will get a better laptop.