0538 GMT June 20, 2019
Britons vote on Thursday on whether to quit the 28-nation bloc amid warnings from world leaders, investors and companies that a decision to leave would diminish British political and economic influence, unleash turmoil on markets and send shock waves around the Western world, Reuters reported.
As each side sought to play its last trump cards, the pro-EU "Britain Stronger in Europe" campaign issued a final poster of a door leading into a dark void with the slogan: "Leave and there's no going back."
And former England soccer captain David Beckham, a hugely popular celebrity, added his voice on Tuesday to the list of Remain supporters. "For our children and their children we should be facing the problems of the world together and not alone," he said.
Leave campaigners meanwhile stepped up their relentless focus on what they call uncontrolled immigration, saying Prime Minister David Cameron had been warned four years ago his goal of reducing net arrivals was impossible due to EU rules.
The EU - already shaken by differences over migration and the future of the euro zone - would lose its second-largest economy, one of its top two military powers and by far its richest financial center.
George Soros, the billionaire who bet against the pound in 1992, wrote in an article for the Guardian newspaper that a vote to leave would trigger a bigger, more disruptive devaluation than the fall on Black Wednesday, when market pressure forced the British currency out of the European Exchange Rate Mechanism.
Sterling has been climbing on recent days on the back of more positive opinion polls suggesting the mood of the public was swinging behind the "In" camp, but even its supporters said the result was on a knife edge.
"Things have improved for the 'Remain' side in last few days but it could still be very close ... I have more confidence over the last few days," Junior Finance Minister Greg Hands told investors at a conference on Tuesday.
An ORB poll for Tuesday's Daily Telegraph newspaper found support for Remain at 53 percent, up 5 percentage points on the previous one, with support for Leave on 46 percent, down three points.
"All the signs of ORB’s latest and final poll point to a referendum that will truly come down to the wire," said Lynton Crosby, a political strategist who advised the ruling Conservative Party at the last national election in 2015.
The "Leave" camp had "failed to quash the almost ubiquitous perception that it is the riskier of the two options," he said.
Social research body NatCen also published a survey that found Remain on 53 percent and Leave on 47 percent, using a method that took on recommendations by an official inquiry into why pollsters got last year's election wrong, although its research was conducted from May 16 to June 12.
However, an online poll by YouGov for The Times showed Leave ahead on 44 percent, up one point, with Remain on 42 percent, down two points.
Campaigning was suspended for three days after the murder of pro-EU lawmaker Jo Cox, who was shot and stabbed to death in her constituency in northern England last Thursday.
The killing led to soul searching about the campaign and its tone, with Jeremy Corbyn, leader of Cox's opposition Labour Party, saying her murder was likely "extreme political violence".
Some "Leave" campaigners accuse the "Remain" camp of exploiting the death as part of what they portray as a campaign of scaremongering over the referendum by the establishment at home and abroad.
Turnout is predicted to be key to the result, and the ORB poll found that Remain supporters, who had been regarded as being more apathetic, were becoming increasingly motivated to vote as polling day approaches.