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.
This blog charts the fortunes of water voles in and around the Whitchurch area, North Shropshire. Water voles are one of the UK's most threatened mammals, extinct in many counties, and so it's vital they receive as much monitoring and protection as there is going. Here in Whitchurch we're lucky enough to have them right in the middle of town - how cool is that?