It's available as a torrent for those outside Blightly.
The Lt Col i/c the new shaft project surprised me. To his great surprise the sand at 8m/30ft deep kept collapsing, so they finally decided that it was too risky to attempt to tunnel into the wartime tunnel both because of the risks to the modern-day tunnelers and also because they'd destroy the old tunnels in the process of trying to break into them.
I'd have thought all that was fairly obvious before he started, but perhaps not?