The material, that was said to be “unknown to science” following tests, was stored in buildings modified by a private aerospace company which was paid huge amounts of money by the US Department of Defense to research the phenomenon and look after the “metal alloys”, according to reports.

However, no images have surfaced of the alleged material, nor have any details of where it was found, or any reports of tests carried out on it.

Details of the $22 million (£16.5 million) top secret Department of Defense Advanced Aerospace Threat Identification programme investigating the threat posed by UFOs, that supposedly looked at the material, was revealed this weekend.

The New York Times reported that the project ran from 2007 to 2012 and the money was used for “management of the program, research and assessments of the threat posed by the objects.”

It was run by military intelligence official, Luis Elizondo, on the fifth floor of the Pentagon’s C Ring.

Mr Elizondo, who resigned to form UFO research group To The Stars Academy with former Blink 182 singer Tom DeLonge's, said that the effort secretly continues and that he has a successor, whom he declined to name.