Power Supply unit help?

Solution
You should not replace the EVGA 550 G2 you selected with the Seasonic S12II as suggested above. While the Seasonic is a great quality PSU it does not support Haswell/Skylake sleep states like the EVGA does. Also the EVGA is more efficient (the S12II is a Bronze unit, EVGA Gold).
Changed out a few components.
No point getting a WD Black in 1TB, as the WD Blue performs the same, just with less warranty.
WD Blacks you typically want to reserve for builds with 2TB of space or more.
Also upgraded you to the AsRock K4, as it is actually 4 pounds cheaper.
Power supply is very good quality, however you can get the same quality for a lower price. The G2 comes from Superflower, which is one of the top two power supply OEMs next to Seasonic. It gains in price due to the reputation of the line however, and they are not necessarily the best value at lower wattages.
Fan is perfectly fine, although you might want to pick up a second one for a bit more.
Posting build in a bit.
 
Edit: It has been brought to my attention by Rogue Leader that the S12II does not support Haswell sleep states despite its near identical modular counterpart supporting such states. This has been edited and reflected in the build now.
Sorry for any confusion! :)
Component selection is on point for the most part, but changed out the K3 for the better K4 which is actually cheaper.
Changed out a few other things for better value as well, but very good job!

PCPartPicker part list: http://uk.pcpartpicker.com/list/jL4zNN
Price breakdown by merchant: http://uk.pcpartpicker.com/list/jL4zNN/by_merchant/

CPU: Intel Core i5-6600K 3.5GHz Quad-Core Processor (£210.00 @ Amazon UK)
CPU Cooler: Noctua NH-D14 65.0 CFM CPU Cooler (£57.46 @ CCL Computers)
Motherboard: ASRock Fatal1ty Z170 Gaming K4 ATX LGA1151 Motherboard (£106.84 @ CCL Computers)
Memory: Corsair Vengeance LPX 16GB (2 x 8GB) DDR4-2400 Memory (£65.77 @ CCL Computers)
Storage: Samsung 850 EVO-Series 250GB 2.5" Solid State Drive (£79.98 @ Ebuyer)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£41.62 @ Amazon UK)
Video Card: MSI GeForce GTX 1060 6GB GAMING X Video Card (£289.98 @ Amazon UK)
Case: NZXT S340 (Black/Red) ATX Mid Tower Case (£69.98 @ Novatech)
Power Supply: EVGA SuperNOVA G2 550W 80+ Gold Certified Fully-Modular ATX Power Supply (£70.97 @ Amazon UK)
Operating System: Microsoft Windows 10 Home OEM 64-bit (Purchased For £29.90)
Case Fan: Corsair Air Series AF140 Quiet Edition 67.8 CFM 140mm Fan (£13.99 @ Amazon UK)
Case Fan: Corsair Air Series AF140 Quiet Edition 67.8 CFM 140mm Fan (£13.99 @ Amazon UK)
Total: £1050.48
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-08-04 14:54 BST+0100
 
Your build is absolutely fine and I don't see why you'd change anything. Any changes you make are pretty much on a like-for-like basis.

You could swap the WD Black for a Blue and save a few quid. The Blacks are faster but you're unlikely to notice and therefore appreciate the extra speed. The extra warranty is nice to have though, especially when it comes to HDDs as they're the most likely components to fail.
 

Yep, I just made a few minor adjustments and changes for different scenarios.
Apart from that it was very solid though! :)
Keep working on your build skills, really good in terms of part selection and value. :D
 

Rogue Leader

It's a trap!
Moderator
You should not replace the EVGA 550 G2 you selected with the Seasonic S12II as suggested above. While the Seasonic is a great quality PSU it does not support Haswell/Skylake sleep states like the EVGA does. Also the EVGA is more efficient (the S12II is a Bronze unit, EVGA Gold).
 
Solution


The M12II is essentially the same as the S12II but with modular cables, and that does support the C7 state.
Was having a conversation about this earlier actually, not entirely clear on what the S12II's specific position is given the near identical specs of the M12II and the S12II.
Is it just that the S12II never underwent testing? Or is there something to this i'm missing?

I guess the EVGA G2 is the way to go for now then. :) I'll edit it in.