Some CDG members may have read Keith Jessop's book "Goldfinder" about recovering £45,000,000 worth of gold from the wreck of the HMS Edinburgh in about 250 m of water in the Barents Sea, over 40 years ago. It's a fascinating story of deep diving adventure, to some extent experimental at the time. 

Keith Jessop was a member of the Keighley Sub Aqua Club, which played an important role in the formation of the early CDG Northern Section. KSAC members were involved in some notable 1960s cave diving exploits, such as the discovery of Duke Street II beyond the Ireby sump. Jessop certainly did some cave diving at one stage; there is a photograph taken in Boreham Cave in the book.

John Cross recently pointed me at a documentary film made at the time of the Goldfinder expedition, which is available on You Tube and well worth watching. It might prompt you to read the book, which has a lot more detail about Jessop's early diving career and also about how he made little or nothing from the venture in the end, as it became mired in legal wrangles. Here's the link to the film:

https://www.youtube.com/watch?v=7jdgleSNrJs

(Only the first 59 minutes cover the HMS Edinburgh story; an unrelated film is tacked onto the end).