"miners from overseas will then be required when this is undertaken."

Not just miners, mining equipment too. We used to have a healthy engineering industry manufacturing, inter alia, machinery and equipment for underground and surface operations in the mining industry - which was virtually destroyed as a result of the wholesale mine-closures of the '80s. Presumably, any deep-mining in the future will involve imported machinery, as we are probably no longer able (and probably don't have the expertise anyway) to manufacture it in the UK.