Ok... no responses so I guess no-one has experienced this before. I did a 30min easy session yesterday and it felt just fine. A bit awkward, but no pain. I had to position the arch of my foot on the pedal to stop my ankle wanting to bend through the pedal stroke (cast won't allow this). I figure the extra blood flow from light activity can only help heal the bone. Just about to do the same again today. I'm back to the docs on monday for another x-ray so it will be good to see if there is any progress. Cast feeling quite loose so I assume the little bit of swelling that was still present has gone down.