Recently there was long thread about the BCA. I can now post possible answers to some of the questions, such as "Why is the BCA still raising membership prices when there is a significant amount still left in its coffers?"
Speaking to the original explorers of the Oxford Extensions in Dallimores, they recommend going with someone who can show you the moves to enter the squeezes. The cartwheel manoeuvre in the turning chamber is supposed to be particularly difficult!