The mud eventually runs out to be replaced by more and more inclined slabs, which were very easy on the way up. The gradient steadily increases until the floor merges into the end wall, and the trickle of water enters from high up. At this point, a couple of holes in the roof have already been passed, but investigation revealed these to be beyond reasonable reach without some fairly serious bolting.
Resurveyed by Olly Betts and Martin Sluka in 2002 [Is this next bit still true in 2023>]: but we don't have an entrance fix so the data isn't currently in the dataset.