Well, I truly love my doctor!! In a strictly platonic patient-to-doctor way you understand. Dr Evans just so happens to be an experienced runner himself, and a sports injury specialist. How good is that?!
It turns out I'm suffering from Pes Anserine Bursitis, which is inflammation of the fluid sac that cushions the bones from the group of tendons that run just below the knee on the inside of the leg.
He said that it should improve with time, which it is, and not to worry too much, but to take it easy and keep up my rest days etc. Apparently this is very common in new runners, and, as I suspected, is probably caused by landing badly on the rather uneven towpath.
So it sounds like I shall be fine, and no permanent damage done, and once my body is used to running, it is unlikely to reoccur.
Sorry if this post seems rather self-centred, it's just that some of you kindly asked about how it went at the doctors.
You know what? You lot are a genuinely lovely bunch of people. You're awesome!!!