SECRET air raid tunnels under a former Southend factory site could be listed as protected by English Heritage.
The three air raid shelters were built below the old Ekco site off Priory Crescent, to protect the factory's 3,000 staff during the Second World War.
English Heritage is considering listing the shelters after an application by the Skipp campaign group.
It could hold up plans by Bellway Homes to build 231 homes on the brownfield site.
Skipp wants the shelters preserved and opened as a tourist attraction.
Mark Sharp, from Skipp, said: “The shelters are unique and we feel they are a massive piece of heritage that needs to be preserved.
“The developers have been trying to pretend they aren’t there. But from our view, the modifications would only have to be minor to accommodate the shelters.
“As long as they are maintained and secured, they could be opened as a tourist attraction.”
If they are listed, the shelters could be deemed Grade I or Grade II buildings, giving them planning protection, but it is thought just an entrance to the shelters would interfere with the planned housing estate.
Brian Ayling, Independent councillor for St. Luke’s, said: “I will fully support English Heritage if listing is recommended.
It will preserve structures of great importance to Southend and, indeed, the history of the defence of our realm.” English Heritage will now speak to the Department of Culture, Media, and Sport – with the Department having the final say on listings.
A spokesman for English Heritage said: “There is no specific time-frame for this process, but we are aware the site is the subject of a planning application.
“Currently, we are unable to say whether the ground above the site would be included within any listing.”
The wait for a listing decision could mean the planning application is deferred, or that a condition is attached to protect the land.
Some local historians believe the Ekco shelters are part of a network of wartime tunnels that lead to the airport, with even a “hospital” for shrapnel victims below Priory Park. But council officers say there is no evidence for this.