I never see people using i3 CPUs, and I have been VERY happy with the performance of my i3-4360 @ 3.70GHz x64. I prefer MSI products when it comes to Motherboards and graphics cards. I still run a beat up old MSI GTX480 and don't have many issues. a 660 or 680 would be more than enough I'd think. For cases and power supply I like Rosewill and I'm using Kingston HyperX FURY RAM. Oh and Solid State is the way to go for storage.

the last time I did much parts purchasing, about a year ago I found Amazon to be the easiest and cheapest route. Not sure if that would hold true for the UK though.