Thanks for the advice and encouragement guys

As recommended, I chatted to Danny at DTD last night. He told me he got from zero fitness to running 5k in nine weeks. Running three times a week. I am going to have an extra five weeks or so more than that. But it is an extra 5k!
Still undecided... but think I am going to go for it. What's the worst that can happen?
If I run three times a week for 14 weeks that's only going to be 42 runs in total. Doesn't sound like a lot, especially as the first 10-15 'runs' will actually be mostly walking.
I won't be having a running partner, it'll all be done on my own. I am going to have to squeeze runs into my family life, so will have to do them at funny times... like 1am and stuff like that.
I'm gonna think about this some more and will post again in a few days. Hopefully to say that I've bought some running shoes and started my training.