At the time, the average ton of coal was costing double to extract than it was worth. Closing the loss making mines was inevitable but the viable mines could have remained open, and would have as there was still the demand for coal.
The Germans do this right, their unions want their workers to have fair share of the rewards and understand that the company must be profitable in the first place for that to happen. British union leaders simply play workers against management for their own gain, then leave both workers and management worse off, but workers get the worst of it.