So further to the slight niggle that cropped up in my calf on Friday I've put C25K on hold to avoid a more serious set back. Booked in with a PT at my gym to get some pointers as to what I can and can't do while waiting for my calf to mend. Thought it might be of use to anyone else who has a bit of a niggle...
Cardiowise it seems that cycling, rowing (within reason) and cross training (as long as you keep you heel down on the cross trainer) can be used and then tonight I was put through my paces on the cables doing resistance work, biceps, triceps, back.
PT finished the session by giving the dodgy leg a brief sports massage which made me yelp quite a bit but hopefully this will get me back on my C25K journey. In the meantime I'll keep reading your blogs for inspiration and tips for the journey.