OP HAS BEEN TWEAKED READ IT
Usual rules, except slightly different. I've used PC Part Picker (hint always use PC Part Picker) so you can localize the builds. I've stuck to my own pricepoints but they should translate reasonably well. The rule about personal perference still stands, you can tweak these builds. I still don't include operating systems or peripherals, add £70-100 for your chosen copy of Windows and whatever you want to spend on peripherals.
AMD Low Budget Feb '15
As with the last AMD system, it's a cheap bare-ish system. However, MX100 SSDs are so cheap right now that it ALMOST makes sense to drop the harddrive, stick with the 256GB for now, and add a cheap graphics card. It's a system on a hard budget but for £400 you get a lot of PC.
Intel Low Budget Feb '15
I'll be honest - this is an entirely speculative build based around the unlocked Pentium. You can hit 4.5Ghz reasonably reliably with an aftermarket cooler on the CPU - I haven't included one but there are several reliable £20-30 ones on the market, look at Coolermaster. It's basically Intel on a budget as much as possible in order to fit a solid graphics card in. I like it as a theory but at this budget I'd probably pick up the AMD machine and add a graphics card.
AMD Mid Range Feb '15
Still slightly over budget, but less so, and now has an aftermarket graphics card. Still not a good machine in reality, but if you absolutely have to have a top end card and you're not CPU bound it's a reasonable build.
Intel Mid Range Feb '15
Cut the costs down and changed from the 970 to the 290x in light of the 970's scalability issues. Basically both of the mid-range machines I have tried to leave as much budget room as possible for when the 300 series launches from AMD.