I have had a more detailed examination by a physio resulting in a suggested origin for my problems and a treatment strategy.
Apparently I have slightly fallen arches in both feet. I also have arthritis in both big toes that has significantly stiffened the basal joint; I have been aware of this for about 10 years but was unaware of the consequences. The physio thinks that this joint stiffening will have exacerbated the change in my gait due to the fallen arches. In particular my foot will rotate inwards excessively as I walk and this rotation will be transmitted through the ankle to the knee. They think that this is the cause of strain on the inside ligament in the knees. After 650 miles these have become inflamed and painful. I am having insoles fitted that should stabilise the foot and hopefully ease the pain.
How quickly the ligaments will heal is uncertain but there may yet be the possibility of my completing some further section of the walk before returning to work on 11 June. That would be great, I would love to do some of Scotland.
Next step is to see the effect of the insoles and further manipulation of the knees. That is next Monday.