xkcd

It's quite relevant if you consider that coal mining is concentrated to a much smaller area really. Besides the destroyed habitat, the pollution, the dangers of sinkholes and the cost of renaturation you also have to contend with rain and ground water constantly filling in the mining pits.

Don't know about the UK but in West Germany's Rhein-Ruhr area, a former coal mining hotspot, the energy used to operate the pumps that keep the water out will eventually be greater than the energy gained from burning all the coal. Can't find a source on the quick but I think it might have happened already. Of course it's not a simple subtraction as all that energy was used to generate more infrastructure and capital that can now pay for the pumps. According to this German source their operation costs around 300 million euros yearly which gives you a rough idea of just how expensive that is.