There were holes everywhere. Some were leading out of the bank and formed a distinctive D shape (with the flat part of the D on the bottom), while others were hidden in the tree roots.
A clear trail led from the sett, back up the bank. There were lots of footprints, but it was very muddy so I couldn't make out any clear tracks.
What an exciting discovery and it just goes to show that you never know what you'll find just around the corner! I've regularly walked within a few metres of the sett, but it was only when I took a different path that I actually noticed it. I'll keep an eye on it and take Bug Mad Girl back there to see if we can spot any more signs of life. Perhaps we'll set up the trail camera and see if we can get any pictures of them.