[Coalboard]

The Coal Authority may not have detailed plans of the workings. You can go to view what they have at the Mining Record Office, Bretby near Mansfield, by appointment. They have a website.
The last thing they will do is admit liability if major subsidences occur, it becomes a long drawn out legal matter then. In general they are supposed to have historical liability for pre 1947 workings but in practice they will do their best to get out of that liability. I'd call at your local solictors for the free advice they are supposed to give