Seen from Britain, it all looks so familiar.

A nation faces a momentous choice. On one side is the safe, status quo option that generates little excitement but promises a steady course. The alternative - a leap into the abyss, a primal howl against the establishment - is running closer than expected, evidence of a burning antipathy in the heartland towards an out-of-touch metropolitan elite.

But the political commentators, the polls and the betting markets all seem to suggest that voters will, in the end, stick with what they know. Crisis averted, if only narrowly.

The comparisons between Britain's June vote on whether to leave the European Union and the US presidential election in a little over a week are hard to miss.

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That Britain stunned the world and voted for Brexit is enough to seed doubt in the minds of stalwart Hillary Clinton supporters who, despite her substantial lead in the polls, will have to ponder between now and election night whether Britain's shock could be replicated across the Atlantic.

It's also enough to sustain the hopes of die-hard Donald Trump backers who believe that the experts, once again, have it all wrong.

The Republican nominee has repeatedly fed that belief, calling himself "Mr Brexit," predicting "Brexit times five" and vowing that "there's going to be a lot of Brexit happening ... A lot of Brexit."

Trump's political case is, in many ways, remarkably similar to that of the pro-Brexit campaign, building as it does on the grievances of those left behind by globalisation, angry about immigration and wistful for a perceived lost moment of national greatness.

The Clinton and "Remain" campaigns also share a lot, with both emphasising the horrors of what would happen if the other side won, and urging voters not to give in to forces of division.

The campaign slogans hint at the parallels: "Stronger Together" versus "Make America Great Again" in the United States; "Stronger In" versus "Take Back Control" in the United Kingdom.

The analogy goes only so far, however.

Even with the race appearing to tighten and with the FBI's investigative disclosures shaking up the contest, a Trump victory would amount to a far more dramatic upset than Brexit ever was, one that would defy evidence from polls, early-voting data and the organisational infrastructure of the two campaigns.

"The political comparison is absolutely apropos," said Marcus Roberts, director of international projects for the polling firm YouGov. "The electoral comparison is not."

As much of a shock as Brexit was, the polls were not far off. In their final surveys before the vote, two major polling companies got it wrong and predicted a victory for "Remain." But two others got it right, forecasting a "Leave" win. Another four had results within the margin of error.

On the day that Britons cast their ballots, the only safe conclusion to be drawn from the polls alone was that the referendum could swing either way. And swing it did - to a narrow but clear 52-to-48 win for Brexit.

The result hadn't been anticipated, as evidenced by the plummeting value of the pound and of global stock markets the following day. But the surprise had less to do with the polls than it did with a collective belief among Britain's political cognoscenti that the polls, if anything, were underestimating "Remain" support. Political betting markets reflected a view that voters would play it safe.

Republican presidential candidate Donald Trump in Colorado. Photo / AP
Republican presidential candidate Donald Trump in Colorado. Photo / AP

Instead, Brits took the leap. The polls, to the extent that they missed their mark, had underestimated turnout among older and less-educated voters in struggling areas, such as the country's northeast, while overestimating the relative turnout in more affluent metropolitan regions, such as London.

Trump and his boosters have argued that something similar will be at play in the United States on Election Day. British politician Nigel Farage, a longtime Brexit champion who has become a Trump surrogate, has said that pollsters may be missing a Trump surge because they do not realise he has motivated to vote a group that normally stays home.

"The greatest parallel between the Brexit vote and to what may happen on November 8 is that Brexit mobilised a large number of non-voters - indeed, some people who had never voted in their lives," he wrote in a recent Washington Post opinion piece. "That was what secured the victory."

Former House Speaker Newt Gingrich has gone further, suggesting there are Trump voters who do not want to reveal their true intentions to pollsters, "just as with the Brexit vote in Britain".

Roberts acknowledged there may well be some "shy Trump voters," but that the numbers in most contested states simply are not there to overcome Clinton's apparent lead.

"For the Trump claim to be right, these polls would have to be wrong by double the margin of error," he said.

Other, more tangible signs that were not available during the British referendum are also working in the Democrat's favour. The breakdown of party affiliation in early voting, for instance, seems to favour her.

"You have millions of voters being banked in Hillary's column. So the mountain for Trump to climb keeps getting bigger each day," he said. "That was not true of Brexit."

Clinton also has an apparent organisational advantage, having devoted vast sums of money and large numbers of campaign workers to her get-out-the-vote drives. Trump has been dismissive of the need for a ground game. In the Brexit campaign, the two sides were fairly evenly matched on the ground.

One significant advantage for "Leave" that Trump lacks is with the media. The pro-Brexit campaign had the country's influential tabloid press firmly in its corner, while other outlets, such as the BBC, tried to play it straight.

Trump stands for a whole set of values - from misogyny to xenophobia - in a way that Brexit did not

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Trump has consistently complained of a media conspiracy against him, while losing the backing of traditionally Republican outlets.

Anthony King, a government professor at Britain's University of Essex, said that Trump and Brexit have an "astonishingly similar" base among those left behind by globalisation and angry at the political class. But the Brexit campaign, he said, had something more.

"One of the reasons that Brexit won was that it was always a respectable opinion to hold even if you didn't hold it," he said.

"Trump stands for a whole set of values - from misogyny to xenophobia - in a way that Brexit did not."

King said he had thought before the Brexit vote that "the risk-averse sector of the population would outnumber the don't-give-a-damn sector of the population."

It didn't play out that way. Could political lightning strike twice, and prove Trump's Brexit prophecy true?

"I'm not persuaded, but I'm frightened," said King, who, like most Brits is no fan of Trump's. "You can't utterly discount that possibility."