Has hallmarks of Crown mineral agent at work, so Crown Estate probably own land, minerals or both. Adit was reopened years ago but now collapsed, could be dug open but not much to see in there and not worth the trouble.
It was just crosscut through water to a bare stope, flooded ladderway with ladders to see is all there is, engine shaft a pile of debris.
Looking at recent photos is seems that the water is backed up enough to flood the floor of stope which was dry years ago
My avatar is a poor likeness.