The email scandal that has suddenly plunged the US election into fresh drama, could have the impact of helping Hillary Clinton's campaign.

The reopening of the FBI's investigation has boosted support for Republican rival Donald Trump, closing the reported nine-point lead Hillary Clinton held.

But Xenia Wickett, Head of the US and Americas Programme at Chatham House told CNBC the scandal and narrowing polls could turn out to be a boost to the former secretary of state.

Xenia Wickett said that Democrats may come out to save Ms Clinton (AP)

“Trump voters are very enthusiastic about Trump so they will come out to vote," she said. “Clinton voters are often not so enthusiastic about her, so if people see the polls are cloning closer together the level of complacency that many hold will be removed and lots of people will therefore come out for Clinton that otherwise might not,” said Ms Wickett.

The suggested came another expert said he also felt the FBI storuy would not change the course of the US election, according to an election expert.

Analysis by Nate Silver’s fivethirtyeight.com found that the ‘October surprise’ stories from the last four US presidential elections had not altered the outcome.

It comes after detectives announced a probe into a cache of private server emails allegedly found on the laptop of disgraced “sexting” scandal congressman Anthony Weiner.

The biggest October surprise would be if this had any bearing on the 8 November climax, according to 538's senior political writer and analyst Harry Enten.

FBI director James Comey, standing behind US Attorney General Loretta Lynch, apparently ignored warnings from the justice department about going public Alex Wong/Getty Images (Alex Wong/Getty Images)

“It will take several days to measure its effect on the race, and the real surprise would be a wild swing in the polls," 538 said.

“That’s because even the most memorable October surprises of recent history weren’t the game changers they’re sometimes portrayed to be.”

Such stories, which can take place in the last few weeks before the election, included the news that George W. Bush was arrested for drunk driving back in 1976 which broke shortly before the 2000 election, Osama Bin Laden's release a video tape ridiculing Mr Bush on 29 October, 2004, the stock market suffering a huge loss on 6 October, 2008, and Hurricane Sandy hitting the east coast on 29 October, 2012.

Anthony Weiner, with wife and Clinton aide Huma Abedin at a press conference, sent a lewd text message to a 15-year-old girl AP (AP)

The article also referenced President Lyndon Johnson’s halting of the Vietnam bombing on 31 October, 1968, and the Iran hostage crisis in 1980.

The same presidential candidate was winning the polls before and after each of these six news stories broke – and triumphed in the real thing.

Mr Silver, a statistician and baseball analyst, successfully called the outcomes of 49 out of 50 states in the 2008 presidential election.

The 38-year-old was named one of the world’s 100 most influential people by Time magazine in 2009.

Donald Trump, speaking at a campaign rally at the University of Northern Colorado, says the emails scandal is 'bigger than Watergate' AP (AP)

His model – of electoral history, demographics and polling – correctly predicted the winner in 34 of 37 contested senate races in 2010.

The Michigan-born journalist also accurately predicted the winner of all 50 states during the 2012 presidential election.

Hillary Clinton email probe: Donald Trump hails decision to investigate new emails

FBI director James Comey said that newly found emails justified reopening an investigation that was closed in July.

A source claimed the emails were unearthed on the laptop of Mr Weiner, the estranged husband of Ms Clinton’s aide of 20 years, Huma Abedin. Mr Weiner was investigated for sending a lewd text message to a 15-year-old girl.

But Mr Comey, who has faced widespread criticism for the timing of the ambiguous announcement, reportedly ignored advice from senior US justice department officials by going public.