That one cant not either.
OK let me just explain something. Your build is completely lopsided and won't be able to benefit from Crossfire any, it NEEDS 8GB of RAM, it NEEDS a good motherboard, it NEEDS a 650W + QUALITY power supply.
Your budget DOES NOT allow you to run Crossfire.
PCI-e is the connector used for a graphics card, to run 2 graphics cards, you need 2 PCI-e slots that are capable of run in x8 (PCI-e x 8 mode).
Since you are on a tight budget, FORGET crossfire.
You are wasting money on it since you need a better motherboard and a better PSU. The CX600 Corsair IS NOT enough for 2 cards.
Also, get 8GB RAM.
I have changed your build to the below, its the most balanced for the price and will give you good performance without the need for crossfire.
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i3-4160 3.6GHz Dual-Core Processor (£84.16 @ Scan.co.uk)
Motherboard: ASRock H97M PRO4 Micro ATX LGA1150 Motherboard (£64.99 @ Amazon UK)
Memory: Crucial Ballistix Sport XT 8GB (2 x 4GB) DDR3-1600 Memory (£57.99 @ Amazon UK)
Storage: Western Digital Caviar Blue 250GB 3.5" 7200RPM Internal Hard Drive (£19.97 @ CCL Computers)
Video Card: MSI GeForce GTX 970 4GB Twin Frozr V Video Card (£274.99 @ Ebuyer)
Case: Corsair SPEC-01 RED ATX Mid Tower Case (£36.35 @ Aria PC)
Power Supply: EVGA 600B 600W 80+ Bronze Certified ATX Power Supply (£43.76 @ Amazon UK)
Case Fan: Corsair SP120 57.2 CFM 120mm Fan (£8.39 @ Aria PC)
Total: £590.60
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-10-03 08:13 BST+0100
The graphics card i added, the GTX970, is almost twice as fast as the R9 270x.
I also added a higher quality power supply.
And 8GB of RAM.