Professor Brian Cox has said extraordinary claims about the existence of aliens were made in a US senate hearing, but were not backed up by “extraordinary evidence”.

US lawmakers heard first-hand accounts of unidentified flying object (UFO) sightings from former members of the military on Wednesday in a hearing to explore what the US Government knows about the existence of UFOs.

Retired Major David Grusch told Congress the US is concealing a long-standing programme that retrieves and reverse-engineers UFOs and that the US likely has been aware of “non-human” activity since the 1930s.

The Pentagon has denied Mr Grusch’s claims of a cover-up.

On Thursday, Cox, a professor of particle physics at the University of Manchester and a broadcaster, tweeted: “I keep being asked what I make of the UFO thing in Congress yesterday, so here it is.

“I watched a few clips and saw some people who seemed to believe stuff saying extraordinary things without presenting extraordinary evidence.”

Cox said he has nothing more to say than “it would be great if true”.

The 55-year-old added: “It would take a bit of the pressure off our civilisation if we weren’t the only means within the Milky Way by which the Universe understands itself.

“Sadly, as of today, I still feel that pressure, so can we perhaps focus on not messing our world up rather than hoping that, to paraphrase Sagan, someone will float down to save us from ourselves.”