For decades, Larry Sanders has been living in Oxford in relative anonymity. Even running in the last general election did little to boost his profile, taking a humble 4.4 per cent of the vote for the Greens in Oxford West and Abingdon.

But one thing led him to stand out. Appearing on local radio back in April during his campaign, Mr Sanders was asked to say something interesting about himself. He started crying and said: “My brother announced just today that he is running to be President of the United States.”

As reporters beat a path to the door of Mr Sanders’ terraced house to question him about this revelation, he predicted his younger brother Bernie, also an underdog, would “surprise people” and “change the shape of US politics”, but fail to beat Hillary Clinton to the Democratic nomination.

Now, he is beginning to re-think that prediction, thinking back to those comments and telling The Independent: “I was wrong about one thing.”

His mind has changed gradually, with Bernie emerging in recent weeks as a genuine contender to Clinton – with one poll putting him five percentage points ahead of her in Iowa, where the first Democratic caucus will be held.

Democratic presidential hopeful Bernie Sanders, speaks to a steelworkers union in Iowa (Getty)

British-based Mr Sanders, a retired social worker and lecturer who moved to the UK in 1968 with his UK-born first wife, said: “It was just a kind of drift, of thinking:‘Oh my God, look what’s happened here, and here. Wherever he gets better known, his standing improves. It’s hard to believe that when people hear about his approach to the issues, they won’t think he is hitting the nail on the head.”

The 80-year-old county councillor insisted this wasn’t merely speaking out of pride for his 74-year-old brother whom, when they were growing up, he called “Bernard, or, more often, ‘hey you’.”

“For my own sanity,” said Mr Sanders, “I am trying to be objective.”

The core of his brother’s appeal, he said, is that his calls for radical reform stem from first-hand knowledge of worrying about where the next pay cheque was coming from, acquired when they were growing up in a Jewish immigrant family in Brooklyn.

“He knows about economic insecurity because he lived it. And economic insecurity is not some outlier issue now. It affects 40, 50 per cent of the population,” he said.

Mr Sanders said his younger brother was now “more than capable of working things out”, so he no longer gave him advice, although they retain a friendly rivalry about their relative political achievements. But the former executive committee member of Oxford City Labour Party, who defected to the Greens in protest at Blairite policies, revealed that his brother had helped him in his own election campaign.

“We had a well-attended meeting with Bernard Skyping from the Senate,” he said.

Mr Sanders is now repaying the compliment, as are his UK-based children Jacob, 46, and Anna, 43. Mr Sanders said he is an active member of the “Oxford for Bernie” group, campaigning for eligible voters to sign up to the Democratsabroad.org website and vote for his brother in the primary for expat Americans.

Had they been alive to see it, he said, his parents Elias and Dorothy, would also have been immensely proud of what “Bernard” had achieved.

In their Brooklyn apartment, the couple kept a photo of themselves posing in front of the US Capitol in DC.

“I find myself wondering what my parents would have said had they known that their son would spend so long working there,” said Mr Sanders.

“That he might one day be in the White House would have been... beyond their wildest fantasies.”