Gamblers raise stakes for a Donald Trump win as countdown for US elections begin

In the final countdown to the US election, Americans and foreigners alike are jostling to bet on a shock Donald Trump victory, buoyed by tightening polls and memories of Brexit.

"Since the news of the FBI reopening the investigation, we're seeing five Trump bets for every Hillary (Clinton) one," says Pat Morrow, head oddsmaker at offshore betting site Bovada.Lv.

Gambling on any election is banned in the United States but Americans can partake via a plethora of offshore, online sites such as Bovada, Betfair or Betonline.

The FBI director's announcement last Friday that his agents were reviewing Clinton's email scandal coincided with a tightening in the polls that have slashed the Democratic former secretary of state's previously substantial lead.

While most experts predicted a tightening of the polls anyway, betting has seen an even more spectacular uptick.

A futures market run by the University of Iowa for research and teaching purposes saw the probability of a Trump win rise from nine per cent about 10 days ago to 40 per cent on Monday.

Around 2,300 players, who can each bet $500 maximum, have invested a total of $314,000, says Joyce Berg, Iowa Electronic Markets director.

There is also a lively trade with British bookmakers, where the maverick Republican's odds are also rising in a country rocked by a series of shock political outcomes since Britain voted to leave the European Union.

"Trump certainly currently has the momentum and from as long as an 11/2 chance just two weeks back he is now closing up on Hillary almost day by day," says Graham Sharpe, media relations director at William Hill.

The British bookmakers, who are listed on the London Stock Exchange, shortened Trump's odds for the eighth time in a fortnight — this time from 5/2, around 28 per cent, to 2/1, 33 per cent, he said.

John Mappin, a 51-year-old British businessman who has spent a lot of time in America, says he is "more confident than ever" of a Trump victory and stands to win just over 100,000 pounds (more than $120,000) if he does.

"The polls are very inaccurate. It's very, very similar to the Brexit situation that was here in England," said Mappin, who owns a hotel in Tintagel, Cornwall and a local newspaper group in London.

Final polls before the EU referendum in Britain gave the remain camp a substantial edge, yet the June 23 referendum ended with a 52 per cent to 48 per cent win for the leave campaign, jolting global markets, sending the pound into a tailspin and forcing the prime minister to resign.

Mappin has bet on Trump around 30 times in the last 16 months at William Hill, putting down the most money right after the businessman threw his hat into the race, sailing down a golden escalator in June 2015.