I've been watching this vole for two evenings, and it's a very burrow-based animal. So I'm thinking this is a female with very new babies she can't leave.
Here's a pretty small adult water vole, busy making burrows like the one in the photo at the bottom. You can clearly see the vegetation's been nibbled round the borrow entrance, too. (We'll assume the vole wasn't responsible for the snack bar.)
Great to see this colony up and running again, though I note that the water by Tesco's is contaminated by diesel again. Last time this happened it came from the lorry park at Grocontinental. I don't know where this spill originates, but I've reported it to the Environment Agency.