In reply to andic:
> I am not a keen cyclist,
I am a keen amateur, amateur being the operative word. I am reasonably fit and pretty motivated to cycle to work. That said we have just moved and my daily commute has gone from just under 8 miles each way to just over 10 miles each way. I simply do not have the energy to do it every day and so far have managed to do 5 journeys in one week as an all-time record.
I would try doing it one weekend and see how you feel. Cycling when you are motivated and doing it for fun is one thing. Cycling, knowing you have a full day ahead, or have just had a hard day is another. And for me, there is the added joy of sleepless nights for young-uns.