Fascinating story on the link from the subbrit site. Looking on Google Earth confirms that much of the track on the later diversion route is still in place. I think the Foxfield Railway people may have picked the wrong branch, they could have had the Cheadle branch, with possible interchange with National Rail at Cresswell, if someone paid for a station, and so have some commuter traffic. Of course it would not be as interesting as the steep gradients and colliery which they have....
But Google Earth confirms that the tunnel and mine will no longer be accessible. It looks like some opencast workings have done a good job of obliterating the north end, and may explain why the tunnel collapsed in the middle. I wonder what these workings were for. It looks rather like sand, and the OS map says gravel pit, with some incredibly messy industrial sites to the north.
But there is an interesting feature at SJ993423, or more precisely on Google Earth at 52°58'41.67"N 2° 0'41.98"W 2° 0'41.98"W, which is circular. Probably not above the railway tunnel, but would it be an air shaft for the coal mine?