I see you said (probably partially in jest) 5 stone overweight on another thread, and we also exchanged pleasantries when I called an MP a "fatty" recently, so I'm guessing that your concern is being a little overweight, rather than being unable to run 5k? Your strategy depends on whether your goal is to run 5k, or is just to be much lighter and generally fitter.
I've not done couch to 5k specifically, but I do have experience of losing a lot of weight, and my older joints (I gather you're not young either) don't tolerate running. I did walking, and lots of it. I did one hour of walking at lunchtime, at least 4 times a week, and another half hour in the evening. It's gentler on the joints, it's really good for fat burning, and it's easy to motivate yourself for. With a half sensible eye on your diet at the same time (portion control being the key), the weight falls off. You can lose 2 stone before this summer, with no stupid diet and no high impact running.