^This is just a simple improved build based on what you posted. You excluded for example a monitor, an OS, and a disc drive so I excluded them as well, assuming that you won't need to purchase them for whatever reason. You could easily make a superior PC for £1000, at least based on the US prices I see aggregated on PCPartPicker.
The above build has 16GB of DDR3-1866 RAM, a superior SSD, GPU, CPU cooler and less expensive case with similar air flow and aesthetic details to the Antec 300. The GPU in particular is tom's hardware's best buy from £120-£180. It's based on the same tahitis as the 79xx series as opposed to the pictairns from the 78xx and thus achieves a higher level of performance and overclockability while staying price competitive with the lower performing GTX 660 ti. You could easily add a GTX 670 if you're more keen to go with nvidia for whatever reason and still stay within the proposed £1000 budget.
At GTX 670 level (probably much lower really) and ~1920x1200 resolution you cease to need a better GPU for DCS World as of 2013 (not to mention some pretty absurd performance in Crysis 3), and therefore money spent on something better performing like a 7970 or 680 is frankly a waste. You could save for a better monitor, a pair of pedals, some beer etc..
You will of course receive a better deal if you buy the parts separately and assemble and overclock yourself, but if that isn't your thing the lists should help anyway. Have fun with your new PC and cheers.
With a GTX 670, DVD Drive and Win7 pro 64: