British astrophysicist Stephen Hawking has waded into the world of US electoral politics and taken a swipe at GOP presidential candidate Donald Trump, calling him a "demagogue who seems to appeal to the lowest common denominator."

The world famous scientist admitted he has finally been stumped by an intellectual puzzle: Trump's popularity, he revealed in a recent interview on ITV's breakfast programme, Good Morning Britain.

It comes as little surprise to learn Hawking is not a fan of Trump. Besides being in an entirely different political camp, Hawking - who suffers from a form of amyotrophic lateral sclerosis known as Lou Gehrig's disease - is an outspoken advocate for individuals with disabilities. Trump drew sharp criticism in late 2015 when he appeared to mock a New York Times reporter with a disability at a rally in South Carolina. Trump later insisted his actions had been misinterpreted.

Trump ripped into journalist Serge Kovaleski after the writer denied being the source of a report imagined by Trump saying that "thousands of Muslims" in New York cheered the 9/11 terror attack.

Trump was criticised for this speech in which he appears to mock a New York Times reporter with a disability. CNN

Hawking's mind was also on a key UK issue. He took the opportunity during his TV appearance to again urge British citizens to vote to keep the UK in the European Union in the upcoming referendum, reports the Metro.

"Gone are the days we could stand on our own against the world," Hawking warned in the pre-recorded interview, that will be aired early on Tuesday morning (31 May).

"We need to be part of a larger group of nations, both for our security and our trade. The possibility of our leaving the EU has already led to a sharp fall in the pound, because the markets judge that it will damage our economy."

Hawking pitched two key reasons for staying in the EU. The first, he said, is that it "promotes the mobility of people," bringing "new people with different ideas, derived from their different backgrounds."

"The other reason is financial," he added. "The European Research Council has given large grants to UK institutions, either to foster or promote exchanges."

Earlier this year, Hawking, in a letter written to the Times, warned: "If the UK leaves the EU and there is a loss of freedom of movement of scientists between the UK and Europe it will be a disaster for UK science and universities."