Natural England / English Nature did issue guidelines on works around badger sets. As I remember, it was no closer than 50m with tracked earth moving machinery, 25m for a backhoe JCB and 10 metres for hand tools.
As you can probably guess by my use of the name English Nature, my knowledge isn't completely up to date.
However, the penalties for disturbing badgers are very high, and there are a lot of local conservation groups around who probably know where the sett is, and therefore that you've disturbed it. The crimes related to protected species include disturbance, which can be creating noise, digging etc. – literally anything that will disturb. Certainly building a trail that passes by a badger set would constitute disturbance – both in building and possibly in use.
To be honest, badger setts are so obvious you'd need to worry about a wide range of people shopping you – dog walkers, farmers etc., not just those in the know. It might not lead back to you, but it'd certainly result in some work to get the trails closed.
My advice would be to re-route the trail so that it passes no closer than 10m to a sett. It's not difficult to work out where they are, particularly once you've seen one, so my advice is to check there aren't other outlying setts nearby before you start digging again. You'll no doubt notice that they like to dig into the side of earth banks.
