Having rested 4 days and struggled up and down stairs with a sore arch on the left foot, I decided to do my leg exercises first and decide whether to run.
They went well, and the pain eased, running at 4, 5 then 6mph and warming down thoroughly.
Fingers crossed it's just muscular and will clear up. No issues running for the 3 x 5 minutes at all, my breathing should improve. One happy bunny!