Edit: After posting this, I realized I forgot you seem to live in the UK. Though, the best bang for buck rule of thumb concerning asus may still hold true there as well.
In general, I have found Asus' G series laptop line to provide the most bang for your buck in terms of specs.
Doing a search on newegg and google with the key phrase "Asus G series", this is the best I found in a couple of minutes.
http://www.sears.com/shc/s/p_10153_...4&i_cntr=1321671657641&sid=IDx20070921x00003a
Though, there might be better deals out there, so I encourage you to do your own due diligence.
Also, sears might charge sales tax, in which case might make the price comparable to the same model sold on newegg, depending on where you live.
It seems to be very similar to the one I got on newegg a mouth ago for 800 bucks, but the one linked to above seems to have a slightly better videocard.
However, be warned that the upgrade process turned out to be one of the most unstreamlined processes for any laptop I have ever owned, but you can get it done with the below video. Also, this laptop tends to be a pound more than other, similarly speced (though more expensive) gaming laptops.
http://www.youtube.com/watch?v=Ev8y8xlCdHE
You can use this video to upgrade the ram as well.
Hope that helps.