Much better to have your own thread, now when someone answers here you will get an email.
As I said its not necessary or even desirable to spend £5k.
One of the most expensive computers you can see is Alienware, made from good components but in my opinion very overpriced. If you're interested look for their website.
My choice is Novatech. click here you do have to add a monitor but you can pick what you like a 19" or a much larger screen if you wish.
Thats a dear PC. And I'm Scottish so personally I would drop my sights a bit and get something like this click here a lot cheaper.
Or if you don't fancy that then have a look here and build your own click here , personally I think what they call their gamer PCs are not really that at all as they start with a 8600GT and while thats a pretty good card its not a gaming graphics card.