There was one of these underground bomb storage facilities near me at Harpur Hill, just outside of Buxton. I belive part of it started getting unstable during the war, causing its abandonment and I've often wondered a) is any of it still intact and b) if so, where might there be a way in? Harpur Hill does still have some connection with big bangs as the HSE have their explosive tesitng laboratory up there.
As for the nerve gas in Wales, it wouldn't surprise me - there was all sorts of unpleasant stuff chucked into the sea post-1945 as a cheap alternative to safe disposal.....
Follow the horses, Johnny my laddie, follow the horses canny lad-oh!