So I used to be a lot fitter ~2 years ago, but I was never a runner (ex-rugby player)
I started running recently to get back in to shape, and in my first week I was just about managing to run non-stop for 20 mins.
I certainly can't run 5k yet, and I want to be able to, so I found this programme, but I don't think I am coming totally from "the couch".
Looking for opinions on whether it is a bad idea to skip ahead and start on a week which will challenge me right from the get-go?
I don't think it would matter if you skipped a bit, except to say that you'll miss out on some of the story, and also some advice from the early sections. I also started out already reasonably fit (regular swimmer and pilates/yoga-er), but was sufficiently interested in the programme as a whole to want to experience it fully. I did, however, push myself faster than the 'conversational pace' suggested, right from the get-go - which is something you could perhaps try yourself.
Anyway, whatever you decide, I hope you enjoy C25K and get what you want from it - and report back here! 
If you can comfortably run say 10 mins or 3 lots of 5 or whatever, then pick a week that is about that level and start there, but perhaps repeat it twice so you get the reps into your legs before progressing. Take it as you feel it, really. There isn't any point in going right back to 60 second intervals if you can run a lot more already though.
For once I'm going to disagree with Rignold. I reckon you should do the whole programme from week 1 but just really push your speed in the early weeks whilst you're finding it easy. Normally speed should be the last thing on your mind during the programme, but if you're already reasonably fit, then why not use the early weeks as a chance to develop your fast twitch muscle fibres. Good luck whatever you decide to do
If you can run for 20 mins then start from week 5, take it slow though..
Week five
There are three different workouts for this week, which are:
Workout one: a brisk five-minute walk, then five minutes of running, three minutes of walking, five minutes of running, three minutes of walking and five minutes of running.
Workout two: a brisk five-minute walk, then eight minutes of running, five minutes of walking and eight minutes of running.
Workout three: a brisk five-minute walk, then 20 minutes of running, with no walking.
I would skip, you certainly have a great level of fitness. Start at week 4 or 5 perhaps and gauge how you feel??
I would do the whole thing. It's only 9 weeks, and it's not as if it's a waste of time. On the contrary.
It's fun Iain, I'm sure you'll you get on like a house on fire with it. Good luck!
One of the biggest problems with learning to run or return to running, is doing too much too soon and getting injured, which is the last thing you want. I contemplated missing out some early weeks but decided that 9 weeks really wasn't too long to wait to get me running 5k with confidence and suitably developed stamina and perseverance. I did much as roseabi suggests and ran at the fastest pace I could sustain (that takes some learning though).
I am glad that I quelled my macho arrogance and completed the whole programme. It taught me patience. Also, there is also nothing wrong with walking intervals, it is a well respected method used by top athletes for distance training.
Good luck.
My husband started running after I had graduated, primarily to support me. He was starting from a fairly good level of fitness as a cyclist and swimmer but hadn't run for many a year. He did a run from W4 then moved on to W5 and through the rest of the programme. All worked fine for him.
Try w1r1. If it's easy, then next run do w2r1 and so on until it starts getting more tricky. Then complete the three runs for that week before proceeding. For the sake of 2-3 weeks it's nopt worth missing too much. It's not macho to start at w5 and end up with shink splints, rather than start at w1 and run injury free to graduation.
Okay, thank you everyone for your input! Opted to start from week 5 as it seemed a nice balance between not being too easy and not pushing myself too hard, and it finishes with a 20 min run which was my starting fitness.
Looking forward to week 6!
Week 1 completed! 
Week 6 Run 1 Complete !!!!! (Early)
Week 1
Week 1 completed
Week 1 completed!
