An absolutely freezing evening strolling up and down the ditch, revealed more feeding signs and this time footprints.
Then, just when I was going to give up, this little creature popped it's head out (the colour has been enhanced).
The following analysis is an attempt to identify it:
Rat: The size and it's locality (in a dried ditch) made me initially think it was a brown rat. Having studied the picture (colour changed and cropped), it lacks the pointed nose and the prominant ears, as can be seen in this picture:
Therefore, it is most likely to be a vole:
Field Vole (Short Tailed Vole): A field vole would explain the feeding signs as (like water voles) they feed on vegetation in the same way. However, they are smaller (10cm) and as the initial identification was a brown rate (22cm) then it is probably too big to be a field vole, as this picture shows (warning, cute picture):
Bank Vole:Bank voles are smaller than field voles (9-11cm), so using the same logic, it's possibly not a bank vole:
Water Vole: Given it's size, it's vole like features, nearby feeding and proximity to an existing water vole colony, the most likely identification is as water vole.
This sighting is now recorded in google maps and although it is near the existing colony, it is far enough away and not directly connected to it to suggest this is a different population of water voles.
View River Ock #4 in a larger map
Identification with assistance from:
About a Brook (http://staggsbrook.blogspot.com/)
Collins complete British Wildlife (1997)