Well now you can add some more people who have been down it. As I said above, a group of us descended it in the 80's using the building which was on the top then as a belay (from the rafters). The description is correct except that (from memory) about 80 feet from the bottom there is a short level/platform/indentation in the shaft which one of our number made the mistake of getting off on. When he tried to get going again the stretch in the rope caused him to plummet.
At the bottom there was water and the level could be seen, but partly due to all the water falling from above and partly due to the anxiety of getting out again, it was never pushed.
The first man down had a GPO telephone operators headset on and trailed the wire behind him. This worked well until he hit the 'step' and the drainage from the Nentforce Level emptied on his head.
It was possible to progress (then) a little way into the Nentforce Level at the top but way too dangerous as the water was running fast and quite deep. To be safe you would need to belay yourself along it.
In any case enthusiasm had waned by then.
I do, somewhere, have a photo of the expedition at the top.
... just found it. It's dated 12/82. So I guess we descended it earlier that winter.
The finest workers in stone are not copper or steel tools, but the gentle touches of air and water working at their leisure with a liberal allowance of time.
Henry David Thoreau