Vandals have been warned against breaking into Second World War tunnels near Newhaven that are lined with a highly toxic metal, known to cause cancer.
The set of tunnels, called HMS Forward, were channelled into a hillside to support vital communications for missions including D-Day.
Now vandals and ‘YouTubers’ are breaking into the maze of pitch black tunnels to take videos and, in some cases, leave graffiti tags.
Jamie Brown, 40, from Eastbourne, is part of the group ‘Urban Explorers’.
Mr Brown said: “Our group go and explore historical sites.
“When we went to HMS Forward we were shocked to see the gates were smashed open and people had been drawing graffiti on the walls. There was even a swastika on one wall.
“It’s such a shame to see something like that ruined.”
Historian and author Geoff Ellis, 84, from Newhaven, was the first person to explore the tunnels after they were abandoned at the end of the war.
After 40 years of research he has written a book and a second edition ‘The Secret Tunnels of South Heighton’.
Mr Ellis said: “I feel quite aggrieved that people are going in and scribbling profane nonsense on the walls.
“People don’t realise that the tunnels are dangerous, they are lined with a highly toxic metal, cadmium.”
“There are grenade pits down there, steep steps and so many twists and turns you could easily become lost.”
Exposure to cadmium is known to cause cancer and targets the bodies cardiovascular, renal, gastrointestinal, neurological, reproductive and respiratory systems.
Over-exposure can occur even in situations where very small quantities of Cadmium are found.
Mr Ellis said he discovered during his research that the tunnels belong to the owners of the houses which have been built on the steep bank directly above them.
English Heritage called the tunnels ‘a site of national importance’ in 2000 after carrying out a survey.
A spokesman for Lewes District Council said this week: “The council is working with other agencies to secure the tunnels and prevent any unauthorised access to them.”