This is probably the best I could see as a starting point:
YOUR BASKET
1 x Gigabyte Z97P-D3 Intel Z97 (Socket 1150) DDR3 ATX Motherboard £61.99
1 x Intel Pentium K Anniversary G3258 Socket LGA1150 Processor - Retail £53.99
1 x EVGA 500W 80 Plus Bronze Power Supply (100-B1-0500-KR) £38.99
1 x Kingston HyperX Fury Black 4GB (1x4GB) DDR3 PC3-12800C10 1600MHz Single Channel Kit (HX316C10FB/4) £32.99
1 x Raijintek Arcadia Mid Tower USB 3.0 Case - Black £24.95
Total : £222.50 (includes shipping : £8.00).
Required:
1 x 4GB of matching RAM.
1 x GPU 6970/7870/270X.
1 x HDD
1 x Heatsink as you'll need a good overclock on the pentium.
I'd buy this one if that was my budget (admittedly a little over). Can take an i7 and GTX 970 later on. The RAM is decent. The 430w PSUs (Corsair/EVGA etc) only bring one PCI-E connector, and most video cards require two, so bear that in mind when it comes to choosing.