I came across this collapsed-looking water vole chamber, but I don't think it had just fallen in naturally because we've had no rain lately, and also some of the bedding had been pulled out. So my guess is digging badgers, or dogs. There were fresh vole droppings inside, though, so there are clearly voles still using the burrow system.
Delighted to see close up this adult water vole with a white spot on its head. I can only assume this is the grown-up baby I saw a few weeks ago. It's not often you can recognise individuals!