I have now really and pedantically completed C25K in that I have actually run 5K on a Park run.
While the C25K programme actually gets us up to a 30 minute run, for most of us this will not be 5K. This is not even slightly a criticism of C25K which I have found absolutely essential in recovering my health after a period of ill-health (trivial ill-health btw - I just had a bad cold in April and in the several months it took to get over the subsequent post-viral fatigue and cough I lost loads of fitness). The C25K program has been really key in getting that fitness back and huge thanks to my coach Reece Parkinson; who according to his script feels we might have forged a bond. Somewhat oddly I think he may be right.
I finished the C25K programme a couple of weeks ago and have been running 'consolidating' runs since. My first Park run was today. As a bit of feedback to anyone doing the same it was tougher than I had imagined. Many people there were very fit and sporting T-shirts of their marathons or running clubs. The general pace was faster than I had imagined (a failure of my imagination really). I tried to take the advice of this forum to go at my own pace but it proved to be tricky to go quite so slowly (no external pressure - just my own).
The whole Parkrun experience was extremely ably managed and I would urge anyone to give it a go after C25K, but be aware it is quite a big step up.