Brains said:
Who said Lumb Hole? You will need more than a JCB for that one! From the entrance in drought follow a blasted crawl for about a 100' to a squeeze into natural...etc...
Yes, thats pretty much the story but in such drought conditions there is a huge, cold draught from the entrance. That can't be coming through the final sump. I think, therefore, that there is a "dry" way forward to bypass the final sump, though it may well be one of the "too tight" leads that you mention.
Digging is not allowed in the cave, (mores the pity) due to alledgedly a rare/unique moss at the entrance.
Just upstream from Lumb Hole is a run in sough that emitts water. It would be a great dig as the mines behind may providea route into natural. No digging allowed there either
Way above Lumb hole are some more open adits/stopes, but they don't go deep enough to hit anything natural.