For a gaming/slight rendering work build you could go for these parts: mobo : MSI z270 Tomahawk - around 135$ cpu : i7 7700k - around 350$ ram : Corsair Vengeance LPX DDR4-3000mhz - around 120$ as for the case, this is always personal but since the parts cost way less than your budget of £1K, I'd say get yourself something good looking. My recommendation would be basically an nzxt s340 or a fractal design define s wich goes for like 85-90$. with this upgrade you might not have to upgrade for a minimum of 3 to 5 years. ( in the end it's just personal if you wish to upgrade sooner than you should )

or you could go for this list if you think you'll be needing a good processor with more core and threads and a slightly worse gaming performance than the i7 7700k. CPU: Ryzen 7 1700 ( you have to overclock this one ) Mobo : MSI X370 GAMING PRO CARBON AM4 for around 180$ ( this is an absolutely beautiful motherboard ) RAM : G.Skill Ripjaws V Series DDR4-3200mhz for around 120$ as for the case you could stick to the same one of course or just get any atx case you like.

To be fair, if you're playing on 1440p or higher resolution i'd go with the second one because the load would be more gpu based than cpu and the differences between ryzen 7 1700 and the 7700k in gaming will be minimal. At the same time you'll still be rocking an 8 core 16 threads cpu so rendering wise you've still made the better choice there. PS: that's what I personally think, this may not be true at all but you asked for recommendations.