In reply to Misha:
> One which shows where the local authority boundaries are so you don’t inadvertently crawl across a T3 boundary.
You can do that much more easily up here in the Three Counties system. Go down Lancaster Hole (Tier 1 Cumbria) and come out of Link Pot or Pippikin (Tier 3 Lancashire). I'm not sure if they've been physically connected yet but, you might be able to pass under the border, dodging the CRO check points and come out of Marble Steps Pot which is in North Yorkshire (Tier 1). It might take diving gear (and a long-term digging project) to avoid breaking the guidelines.