At Physio this morning. Injury almost certainly caused by racing/poor prep/imbalance.
JC noted that my left calf muscle in 3/4 size of right , so certainly part of the issue.
Area on inflammation 4C warmer than other right side, not good, but no signs of stress fracture, so that's a positive.
Plan is to completely rest untill no pain and then a suitable strengthening program to get rid of imbalances.