Thanks for everyone's thoughts, I have a number of things to look for on a return visit. It was New Year's eve afternoon, with not a lot of light, One would need to be careful in getting any closer, it would involve climbing over the Coal Authorities fence, which I shall not be doing; the shaft is collapsing as can be seen under the building.
My initial thoughts were about a winder, but the coal would have gone straight out of the adit to a mineral railway. There is a scatter of small coals at the edge of the shaft, I wondered about a shaft top furnace to draw air through the pit, I believe that they were still in use at that time. If it was a generator house to supply electricity to the pit, would they have used steam to power a generator?
Any other thoughts will be welcome, I will have to try and get back there on a sunny afternoon and see if there is any more to see.