Back from the physio, with good news and bad, the diagnosis is a strained soleus muscle, probably due to the cold weather on Saturday during the long run (-7).
First the bad, no Wokingham this weekend as it would be too soon with the possibility of tearing the muscle
Now the good, it is only a strain so I can still run so long as I am not pushing, so I will learn running easy. Also so long as I follow the advice, which I will, I should be back up to full speed in 10 days.
A progression 6 tomorrow to find the easy pace