Earth may well have been visited by objects from outer space, the former head of a secret US government programme has told The Telegraph.

Luis Elizondo said the existence of supremely advanced unidentified aircraft, using technology that did not belong to any nation, had been "proved beyond reasonable doubt".

Until two months ago, from his office on the fifth floor of The Pentagon, Mr Elizondo, a career intelligence officer, ran the innocuously named Advanced Aviation Threat Identification Program (AATIP), which was funded with $22 million in "black ops money" from Congress.

The existence of the real-life X-Files department, which began in 2007, was revealed this week and confirmed by the Pentagon.

In an interview with the Telegraph Mr Elizondo said much of what he could discuss was still classified.

That included whether his team had examined UFO sightings in other countries including the UK, or spoken to witnesses there.