On 1 February, Bernie Sanders will face Hillary Clinton in the Iowa caucuses, the first electoral battle to determine the US Democratic Party’s nominee in the run-up to the 2016 presidential election. A 74-year-old, self-described “socialist”, Sanders has defied great odds. Some polls even put him ahead of Clinton in Iowa and his odds of winning the nomination have fallen as low as 3/1.

Some 4,000 miles away from Iowa, Sanders’s brother will be cheering him on. Larry Sanders moved to Britain in 1968 after meeting the woman who became his first wife, yet he has remained close to his brother, personally and in politics. “We agree on an astonishing number of things,” Larry, a former UK Green Party councillor who ran unsuccessfully for parliament last year, tells me over tea in his snug kitchen in Oxford. “Our underlying sense of what political life should be about hasn’t really changed.”

Larry is six years Bernie’s senior and retains the same distinctive New York twang. He describes the Sanders brothers as products of their upbringing in 1940s Brooklyn. “Jewish boys growing up in New York knew a lot about Hitler and they knew that politics is not a thrill. Politics is deadly serious.”

Bernie (always “Bernard” to his brother) has described Larry as the one who “introduced me to a lot of my ideas”. Larry says this is “overdoing it”. “I learned things and we talked about them, but we talked more about baseball than politics.”

While Larry built a life in England, working as a social worker and for an NHS mental health trust, he watched Bernie’s political career unfold. After seven years as chairman of the left-wing Liberty Union Party in the 1970s, Bernie became America’s most successful independent politician, serving in the US House of Representatives for 16 years, then as senator for Vermont since 2007.

“Well, of course,” Larry says, when asked if he is surprised by the trajectory that Bernie’s career has taken. “He’s astonishingly hard-working and has been accused of being a monomaniac in this sense – but it’s not true. He’s a good family person . . . The main issue he’s grasped is the redistribution of income. He’s very boring. You hear these speeches over and over again. People say, ‘How can you say the same thing over and over?’ He says, ‘There are some things that are very important and have to be said.’”

After spending five weeks campaigning for him in Iowa and New Hampshire, Larry is adamant that his brother can win. “In large parts of the country there are people who barely know his name. There’s a whole untapped reservoir.”

“Winning the nomination is the hard part. When he’s won the nomination he will win the presidency. I think he will get similar votes to Hillary Clinton from the Democratic base, but because he’s running a class-based campaign he is saying to Republicans, ‘You may disagree with me on gay marriage, you may disagree with me on abortion, but if you would like to have a decent life for you and your children you want to listen to what I’m saying, because I’m on your side.’”

Even if he doesn’t win, Bernie has already had a big impact on the race. Larry recalls Bernie’s first political contest, for president of the high-school student body, at 17. Bernie came third out of three candidates, but the winning candidate adopted his policy to raise money to provide scholarships for Korean orphans. Should Clinton win the nomination, she will run for president on a more left-wing platform because of Bernie’s influence. Yet this prospect is not enough to satisfy Larry. “Let’s do another interview,” he says as I leave, “next time from the White House.”