Sorry for digging up old post.
Reading through Kent council website found out about tunnel network under beacon hill Chatham. Close to Luton wreck. -
http://webapps.kent.gov.uk/hbsmrgatewaykent/DataFiles/Docs/AssocDoc38036.pdf
“
Beacon Hill Radio Station: This was the main transmitting and receiving station for the Chatham naval base from the Second World War until closure in 1982. All surface structures, with the exception of one mast and an ancillary building have been removed. However, there remains an interesting complex of shelter tunnels that appear to date from the cold war revival period in the late 1970’s.
Recommendation: Consideration for listing.”
Then have a look on google maps at beacon hill. Follow it up past the top of the hill into the newish builds in ward view just off ash tree lane. Look at the dead end. Look towards chalk bank, concrete/war time hand rails etc. I’m pretty sure that’s where the entrance is and to get to it just at the top of ash tree lane there’s a gate which I believe is the entrance.