Conspiracy theorists claim the Government is stalling and using any excuse to stop the release of the files as they may contain a smoking gun piece of evidence about alien visitations of Earth.
Last year the 18 files were sent to the National Archives for release to the public, but then mysteriously sent back to the MoD for further censure.
The latest release date was set to be this March, but, again they failed to materialise.
Now, the National Archives has blamed the upcoming general election - called to give Theresa May a mandate for Brexit - for further delays, according to Grenzwissenschaft-Aktuell.de.
They are believed to date from 1971-76 and 1996-2000, and 2004.
It is also hoped there are further files from the December 1980 Rendlesham Forest UFO incident that will shed more light on the bizarre case, when US military officer claim to have seen a UFO land.
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