One of the team who did the photo survey seemed keen on keeping the find quiet
That seems to have back-fired then, if it's at risk of getting filled in now!
Surely a cave discovery on a development site which is clearly at risk should have been publicised as much as possible, as soon as possible. Get the media down there, get a TV archaeologist down there, get the local community excited about it and it would stand a far better chance of surviving.
Other than for particularly significant archaeological finds, the usual requirements for planning are simply to record what was there. It is incredibly rare for an archaeological find to actually block a development in order to preserve it.
Surely now is the time for these stunning photos and lidar survey to be splurged all over the internet, so people can see what's at risk!