The historic observation post, which is near the South Cliff golf course, was boarded up by Scarborough Council workers after the Evening News learned that teenagers as young as 14 were entering the site.

These photographs, which were taken just before the bunker was sealed off, show how dangerous it could be to trespassers.

John Riby, the council's head of technical services, said: "Although we are unsure which agency is responsible for the bunker, in the interests of public safety, council operatives sealed up the bunker. I am disappointed to hear that the work has since been vandalised and I am concerned that an open bunker of this nature is potentially dangerous.

"We will therefore be looking into ways in which the bunker can be sealed in a more robust manner while still allowing for any ventilation that may be required."

The council's conservation officer, Chris Hall, has been able to shed more light on the bunker.

He said: "This site is a Royal Observer Corps monitoring post from the Cold War – not World War II.

"The majority of these sites were built between 1956 and 1964, although their construction began after 1925 and continued into the early 1970s.

"This one is thought to have been built in the 1950s."