The 5C and 5S will both drop in price in five months. Perhaps more than last year's model usually drops due to the fact that larger iPhones are coming - these might set a new standard due to which the used price of the 4" phones might go down faster than has been the case so far.
I'd hold out for five more months to at least see what happens when the iPhone 6 comes out. You'll then get a cheaper 5C if you want, or perhaps a 5S at what is currently the price of the 5C. Or maybe even a iPhone 6 if you happen to be better off then.
Note that I'm speaking from something of a personal bias though... I got the Note 2 five months before the Note 3 was released, and I'm still kind of hitting myself for it
Alternative: just for the hell of it you could go to a store and check out the Nexus 5, which is arguably the best looking Android phone to date, more capable than the iPhone 5C, at half the price. It costs £240 off contract. I thought Android was utter crap until I actually gave it a shot one year ago. Before that I had only used iPhones.