With that sort of budget I think it would be a good idea to build around the i5-6600k CPU, with a Z170 motherboard, 16 GB DDR4, 250GB SSD (for Windows and games), 1TB HDD (for storage), 550W or 650W Gold rated PSU, custom cooler. Approximate cost of all this is about £550.
For GPU the best bang for buck looks to be the new AMD RX 480 at around £200 which should be good for gaming up to 1440p. It's due to be released very soon.
Case, mouse and keyboard are things of more personal preference. Allow about £120 in this area.
Windows 10 adds another £80.
This leaves you about £250 on your budget for a monitor, which should get you a 27" 1440p or 1080p monitor.
Nothing is truly future proof, but something of this sort of spec should last a long time and can be upgraded further in the future if desired (eg i7-6700k, more powerful GPU, more RAM etc).
I've deliberately not listed specific products, as to get the most out of your budget it's probably a good idea to keep an eye on the daily and weekly deals here and special bundles which can bring you some savings.