Bethel Quarry, Bradford on Avon
Ok, so now this is out, I'll add my take on it. Visited with many, including Lenston, OT, Rigsby, Tumbles, Idavoll etc. Sorry if I've missed you out.
Here's some history lifted from OT's report, lifted from the MCRA site

A fairly small (120,000 square feet total area), single adit entrance Bath stone quarry. The Bethel quarries were extensively worked by Messrs. Rogers according to the Bradford on Avon Gazetteer of 1868. It was later requisitioned in 1939 by the War Department and used for Royal Naval storage after some strengthening work. It was later used by Oakfield Farm Products as a mushroom farm and before that had been used by Heinz to grow mushrooms for its mushroom soup. Mushroom production stopped in September 2010 and it was offered for sale in April 2011 as having potential for underground storage. The Estate Agent details reported a "large and historic stone quarry extending to very approximately 10 acres with mains power, water and sewerage connected. The quarry ceased to be mined for stone at the end of the 19th Century but was latterly been used for the farming of mushrooms, though for some months has been disused.
Please take note of the warning on OT's report regarding the recent incident.
On with some pics
The general scene
Canteen
Wash up and stores
Trolleys
Weighing in
This became quite apt

All areas had their name
Selfie (of course)
Think quite a few have seen this now. Still open if you fancy your chances with the local goon.
Thanks for looking.