Good news. I felt I should run after a week off so on monday I did one hour run around the village green... just nice and gentle... feeling out the injury. It was stiff and sore at first but the discomfort got now worse so I carried on. It seemed to ease. I iced it afterwards and the next day there were no ill effects... a little stiff but certainly nowhere near as chronic as previously.
On wednesday I went out on road and did a 65 minute marathon pace run of 15k or so. I concentrated on my foot feeling balanced and flat as it hit the floor (to counter any possible pronation). Good result again...
Looks like the boy could be back in the game.