As an example - with high specs included for memory/hard drive on any of these builds (which can be scaled back), this is what your money could get you.
£1025. I5 processor, 1060 graphics card.
https://www.overclockers.co.uk/ocuk...P2.vZbjQQ2u1ZbjRe2.w*bkeO2.##bkpS2-+*bkqL2-)~
£1136 I7 processor, 1060 graphics card.
https://www.overclockers.co.uk/ocuk...P2.vZbjQQ2u1ZbjRe2.w*bkeO2.##bkpS2-+*bkqL2-)~
£1315 I7 processory, 1070 graphics card.
https://www.overclockers.co.uk/ocuk...P2.vZbjQQ2-ZXbjRe2.w*bkeO2.##bkpS2-+*bkqL2-)~
That £1300 machine is about the most that money can buy at the moment on your budget (although with memory/hard drive configs scaled down, you could probably increase processor/graphics options further on different builds).
What would I do in such a situation? Well, the I5 is a great processor and has 6 cores, but the hyper-threaded I7 does run faster and is more future proofed (both are brand new chip as well). I hate the word future proofed, because we're often proved wrong, but on processors we're now moving quite slowly and actually single core performance really isn't improving much at the moment. I'd be perfectly happy with the I5, which is more than sufficient for most peoples needs, but the I7 is a good chip too so it's about preference and affordability.
The 1060 is the best priced "value" card at the moment (value/budget being a loose term because it's selling for more than twice its MSRP because of the supply issues relating to mining demand). The thing is the 1070 is great, but it's in a different category really. It is a high end card, and high end cards are power hungry and age quickly for the price point. The 1060 can play almost any game out there on full settings at close to 60fps. That makes it in my eyes the stand out graphics card in the market right now and the 1070 a waste of upto £200 extra. In 18 months or so, in all likelyhood that £200 will actually buy you a new graphics chip that is better than the 1070 (if you need to, the 1060 should remain more than adequate by then).
It comes down to choice, what you want it for, and budgetary constraints. In my world, the £1025 machine is perfect right now, but the I7 upgrade could be worth it for heavy usage. The 1070 upgrade simply isn't worth it because of the gpu shortage atm.
If you have £1300 to spend now and don't plan/want to think about upgrading later, spend £1300. But it is probably wise to spend less.