https://order-order.com/2019/03/14/m...amed-big-phil/
We have had threads on this before.
After Dunkirk most southern airfields had tunnels under the runways filled with explosives to be able to deny them to the Germans if an invasion took place. It was done hurriedly and no records kept, and they were then forgotten.
Once some were found in the 1980s as airfields were decommissioned it was realised that hundreds of industrial parks and housing sites could have these still in place, but no knows where. So they kept quiet on the basis they handed gone off so far and, hopefully, had all degraded so they weren’t a risk.
So “Big Phil” is somewhat of an embarrassment. You would have thought it would have found....