Keith, if coal mines were in for a comeback, all the development projects for settlements in East Kent would need be cancelled.
Taking into account that ignition of underground coalmines to exploit gas has not been developed, and could have catastrophic consequences equivalent to a thermo-nuclear explosion if something went out of control, for example if unexpected underground oxygen caused an explosion, then the only option would be to dig the coal out of the ground, or employ open-air pits.
DDC would hardly go ahead with a core strategy to double Dover's population if the Government had an eye on Dover's coal reserves.
Unless of-course the energy strategy changes, Gov. does a u-turn, and opens pits at Whitfield.
