If you find any of these - http://www.bibleandscience.com/science/images/trexfootprint.jpg - however, do the following: a) Run like hell, then b) report to the EA soonest, for they belong to a predator of an altogether different and greater order, common on rivers (or at least in the minds of those who fish them for barbel) like the Wensum and Great Ouse, the Tyrannosaurus Rex.
Robhale, thank you for the information, the sketch of otter prints looks very similar to a print I saw today on a North Yorkshire river bank. It was on a length where otters have been seen.