Alfred:
A couple of points, first it is actually not necessary to have the ground sink. Sometimes (as when mining under Duisburg) it is something that is wanted, other times, such as mining under the aircraft plants in Coventry, it was not. In the latter case they blew washery waste into the hole left as the supports moved forward, back filling the hole, so that the ground moved imperceptibly. (The story I was told was that the precision lathes were only stopped for recalibration once, and off-line for a day).

In regard to automation of mining, the Remote Operation of Longwall Mining Project ran in 1964. All the equipment on the face was automated, with no-one there. There were some teething troubles, but in the end it was closed because of union opposition (local Union said it was fine, National Union said it was fine, Area level union said no dice, as I heard the story), rather than because of technical show stoppers.

Bear in mind that many of the mines were kept open after Nationalization as part of the social compact and that coal could be purchased more cheaply from abroad by the time of the 60's. With a typical mine employing more than a thousand folk, the transition had to be handled somewhat carefully to allow the development of alternate jobs. Which arrangement went by the wayside during the Thatcher years.