The parts for that build come to $830 at Newegg, compared to about $1,130 converting pounds to dollars for yours. Not the best comparison, but you have a general idea of the difference between this buy and an equal build. You could take the parts list and price them out at a web site you might actually purchase from. It's a good experience.
As for the build itself, the processor and mobo are "fine". The cooler is stock (comes with the processor), so OK for normal use. You can do with a cheap case when on a budget. The graphics card is rated "Good 1680x1050 performance in most games" from this monthly article:
http://www.tomshardware.com/reviews/radeon-geforce-price,2323-2.html
so it depends on your screen, "Good" = "OK but not great" (read the article) but it is really light-weight when compared to the processor and mobo.
The power supply unit is not a brand I would recommend, nor is it properly sized for any expansion. This in itself is not a major problem, since it will run. But moving up in graphics and/or pressing a few keys to mildly overclock your PC could be problematic.
Which gets to hello_world's point, your opitons:
You would be spending more money than you need to get this kind of gaming performance. Its out of balance. A cheaper cpu/mobo would allow more money for a better graphics card and the other parts you may need to finish the build. And you'd have a better gamer today. But don't buy yet, wait a couple months for the new i5s which will either be superior, or reduce the cost of alternatives. Either way you win.
Or spend more now and build a far superior machine. Your i7 build gives you much more room for growth. But you'd have to replace your cooler, psu, and graphics card . . . and then your case might not cool well enough. Prices at Arbico for these kinds of upgrades are . . . high.
Or you could buy the Arbico now and upgrade yourself when needed. But you'd be paying twice and faced with doing a good portion of a "new build" by yourself anyhow.
He just said it in 2 sentences, it took me far longer