I do have definitive knowledge of this area.
There is massive confusion of the mine names here.
The entrance shown in these photos is Hag Mine also known as Didos. It is about a 400 foot long stope, with a walkway above a flooded rift and two big pumping shafts. The clear thermal water made for marvellous diving conditions and it was a favourite of SUSS. It was walled off in c.1980 because it is in Council-owned land. This is a great pity - it ought to have been gated. At the time, I suggested that it be made into a show cave.
Nether Hag Mine is often wrongly called Didos by cavers.
This is the big rift entrance by the weir in the grounds of Willersley Castle. I visited the entrance recently and it is still open.
This was where the rescue of a trapped boy scout was made by Lynn Willies, Terry Worthington et al. It was explored by cave divers of Orpheus who published various surveys in their newsletters. Beware that early surveys show a side passage in a sump on the wrong side, which could prove dangerous to explorers. This is the big system with flooded coffin gates and various sumps. The extent of these workings under Willersley is not clear, they seem to sump more and more as one gets further in. I have not heard of anything being done here in recent years.
I am preparing a book for publication on the mines and caverns in the Matlocks and if anyone knows of any further exploration here beyond what Orpheus have published, I would be pleased to be informed about it.