I came across a book a few weeks ago in Sue Ryders (Spalding) about the Cambridge coprolite industry which I almost bought!!

This arose from a conversation with a friend: how many old UK counties can you name that you are sure had no underground mining at all?
When you remember that unlikely places like Hertfordshire and Norfolk had u/g workings, it seems there were not many

I spent an interesting few hours [when I should have been doing something else] looking at all the old counties of the UK. I think there is some evidence of mining in all the English, Welsh & Scottish counties with the possible exception of Selkirkshire - but I stand to be corrected. This includes a well documented coal/lignite mine near Gravesend, so maybe Greater London is in there too.