New PC

[AwkwardSquirtle]

Budget: £1000- ~£1200, potentially willing to go slightly higher
Resolution: 1920 × 1080
Games / Settings Desired: Mostly WoW, HotS, would like to have the option for new AAA titles
Any other intensive software or special things you do: None
Country: UK
Parts that can be reused: None
Do you need an OS: Yes. (Friend recommends Windows 7 over 10, thoughts?)
Do you need peripherals (e.g. monitor, mouse, keyboard, speakers, etc)? Should only need a keyboard.

Have been looking at this site who build the PC for you, which seemed to come out at a comparable price to building it myself.
The Build there is
Case: Aerocool Aero-1000 Black Gaming Case (£60)
CPU: Intel Core i5-6600 SkyLake 3.30 GHz Socket 1151 CPU Processor (£205)
Memory: 16GB (2 x 8GB) HyperX Black Fury DDR4 2666MHz Memory Module Kit (£75.35)
Motherboard: MSI Intel Z170A NVIDIA SLi Skylake ATX Motherboard(£120)
HDD: 1TB Seagate Barracuda 7200 RPM 64Mb Cache Hard Drive (£49.99)
SSD: 240GB Kingston SSDNow UV400 SSD Solid Hard Drive (£65.00)
CPU Cooling: Cooler Master Hyper TX3 Evo CPU Heatsink (£25)
Graphics card: MSI GeForce GTX 1070 ARMOR 8G OC Graphics Card (£400)
Power Supply: 700W - Cooler Master B700 Power Supply (£86.11)
Wi-fi adapter:Asus PCE-N15 IEEE 802.11n PCI Express Wi-Fi Adapter ,300 Mbps (£15)
DVD:Samsung 24x Black Internal DVD RW Writer (£15)
Keyboard:HP Wireless Classic Desktop Keyboard & Mouse Set (£20)
OS: Microsoft Windows 10 Home Edition 64 Bit Operating System (£90)
Total £1,236.45
Thoughts?

[Thunderball]

You need 6600K with a Z170 mobo, bad case, VERY bad SSD, bad cooler (just get the 212 EVO), bad PSU, I would change the wireless card and motherboard. Would look like this:

http://www.box.co.uk/cubesystemconfig/id/63676-G8C3 £1,289.26 with VAT.

I can save about 65 EUR here by buying Windows off Kinguin. Here is what you can build conventionally:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-6600K 3.5GHz Quad-Core Processor (£210.00 @ Amazon UK)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (£29.49 @ Ebuyer)
Motherboard: Asus Z170-A ATX LGA1151 Motherboard (£127.43 @ Amazon UK)
Memory: Kingston FURY 16GB (2 x 8GB) DDR4-2400 Memory (£69.98 @ Novatech)
Storage: Samsung 850 EVO-Series 250GB 2.5" Solid State Drive (£81.84 @ CCL Computers)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£45.48 @ Ebuyer)
Video Card: Palit GeForce GTX 1070 8GB JetStream Video Card (£379.98 @ Ebuyer)
Case: Phanteks Enthoo Pro M ATX Mid Tower Case (£59.83 @ CCL Computers)
Power Supply: EVGA SuperNOVA G2 550W 80+ Gold Certified Fully-Modular ATX Power Supply (£70.97 @ Amazon UK)
Optical Drive: Lite-On iHAS124-14 DVD/CD Writer (£12.20 @ Amazon UK)
Wireless Network Adapter: Gigabyte GC-WB867D-I PCI-Express x1 802.11a/b/g/n/ac Wi-Fi Adapter (£29.75 @ Amazon UK)
Keyboard: Logitech K120 Wired Standard Keyboard (£14.60 @ Amazon UK)
Other: Windows 10 - Kinguin.net (£24.99)
Total: £1156.54
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-08-25 03:25 BST+0100

Also has a better case and motherboard.

[Mythbredor]

Okay so, here's my recommended build for you. First off windows 10, if you're buying an OS new just go ahead and get 10. It has quite a few nice features and improvements and I've had 0 issues with it so far. You can save some money if you'd like buy not buying the keyboard I suggested, it's nice but pricey. And what you listed is a wireless keyboard/mouse set, not just the keyboard. And I honestly can't ever recommend using a wireless keyboard unless you're couch gaming. The HDD and SDD are personal prefrence on the brands atleast, the segate HDD in your build is fine the SSD however is ehh. You don't need a 700W power supply for what you're doing. Do you need a DVD drive? Do you really need wireless?
And as Thunder said you can save some money by buying your key on Kinguin (Disclaimer Kinguin operates in a "grey" area on the market their keys may or may not work, I personally have never heard of any issues with them but just a warning)

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-6600K 3.5GHz Quad-Core Processor ($219.99 @ Newegg)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($24.88 @ OutletPC)
Motherboard: Asus Z170-A ATX LGA1151 Motherboard ($150.88 @ OutletPC)
Memory: G.Skill TridentZ Series 16GB (2 x 8GB) DDR4-3200 Memory ($89.99 @ Newegg)
Storage: Samsung 850 EVO-Series 250GB 2.5" Solid State Drive ($89.39 @ Newegg)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($47.49 @ OutletPC)
Video Card: Gigabyte GeForce GTX 1060 6GB WINDFORCE OC 6G Video Card ($269.95 @ B&H)
Case: NZXT S340 (Black/Red) ATX Mid Tower Case ($64.99 @ SuperBiiz)
Power Supply: EVGA SuperNOVA G2 550W 80+ Gold Certified Fully-Modular ATX Power Supply ($79.49 @ SuperBiiz)
Operating System: Microsoft Windows 10 Home OEM 64-bit ($88.88 @ OutletPC)
Keyboard: Corsair STRAFE RGB Wired Gaming Keyboard ($142.99 @ Best Buy)
Total: $1268.92
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-08-24 22:36 EDT-0400

[AwkwardSquirtle]

Thanks both for help. Went for Thunderball's build on the site I was using, have ditched the wireless keyboard for a wired, and have gone win10 as you recommended.