If you are not planning an overclock then a good brand 80 gold should be sufficient.  Corsair and OCZ are my personal go to units. Would be worthwhile looking at modular units too imho.

THis one is reasonable:

http://www.amazon.co.uk/Corsair-CP-9020056-UK-Series-Modular-Supply/dp/B00FG9FZS2/ref=sr_1_1?ie=UTF8&qid=1404302243&sr=8-1&keywords=850w+gold+psu

If you plan to overclock, you are probably looking at something in the 1000w range.

http://www.amazon.co.uk/Corsair-CP-9020062-UK-Series-RM1000-Modular/dp/B00FLVIQQ8/ref=sr_1_1?ie=UTF8&qid=1404302569&sr=8-1&keywords=1000w+gold+psu