When you're spending that much money on a PC I'd be reluctant to buy from ebay because if anything goes wrong further down the road then you may have a difficult time getting any support from the seller.

I quickly built a computer on Cougar Extreme's website there with:

i5 3570K

8GB RAM

Nvidia 680 GT

256GB SSD

1TB HDD

and it came to £1100. Make sure when choosing your Power Supply that you go with a good branded one. Avoid PSUs made by CiT and Powercool for example - they're not very good.

As already mentioned, avoid Ebay builds. They tend to have a couple of haedline items, like i7-3770K (that's pointless, for gaming) and GTX 680, which, while very potent, is poor value, and then make the rest out of total rubbish components, to get a low price. Something, like that suggested, by D@ve, would be much better. Even then, unless you are gaming at super high resolution ie 1440p or above, the GTX680 is not as good value as the GTX 670, which has almost the same real performance, at substantially lower cost. Another good place to look, assuming you REALLY don't want to build, yourself, is Chillblast. Even they tend to use some basic quality components, but if you pick a base unit, slightly inder £1000, it leaves you some scope, when "customising", to "upgrade" with, say, better case and PSU. Personally, I think you would be best to start with i5-3570K and GTX 670.