Simon
Looking at the caption to the below photograph
[photo]Conglog-Slate-Mine-User-Album-Image-38365[/photo]
can I advise that the level you can see does connect with surface and is easily entered. For information you can aslo descend a roofing shaft into the very top of this chamber. Its bolted but does entail an interesting re-belay (with nothing to stand on) where the shaft breaks into the chamber.
Jon