Hello John
In my over excitement I failed to use my usual scale. I would estimate the larger of the tracks as about 35 - 45 mm. Interesting point about likely differences in "fledging" (?!) size though John.
I now realise that this alone should have suggested mink. It seems that no matter how often I remind myself of the actual size of otters, I still continue to underestimate them!
The other characteristic alluded to by my adviser was the absence of any impression of the distal web.
After referring to a couple of books, (Hamlyn and Oxford guides to Animal Tracks & signs) it seems that the possible variability of imprints in different media could be very misleading. The evaluation of imprints showing a web or not and the continuous or separate imprints of claws seem to require far greater experience than I currently have.
His comments on the scat were that it appeared to contain crayfish remains and would not id otter or mink. He suggested that the only method he knew of (apart from DNA I suppose) was to seal in a plastic bag for a few days. He suggested that the resulting smell would really stink with mink but the otters would smell sweeter. Apparently this was an accidental discovery after forgetting samples left in a jacket pocket.