The Leave camp has a "very strong chance" of pulling off one of the biggest political upheavals of recent times, Ukip leader Nigel Farage insisted as torrential rain threatened to hit turnout in the knife-edge EU referendum.
Speaking outside his Kent home, Farage told the Press Association: "Actually I do think we are in with a very strong chance, I do genuinely.
"But it's all about turnout and those soft Remainers staying at home."
Prime Minister David Cameron ignored questions about the weather, saying only "Good morning" to the gathered media from across the world, as he and wife Samantha cast their votes at Methodist Hall in Westminster.
With turnout seen as key to a result that polls place as too close to call, unseasonal downpours across London and the South East could impact on voter levels as bad weather tends to have a negative influence on the number of people who cast their ballots.
Labour leader Jeremy Corbyn arrived in a positive mood to cast his vote at Pakeman Primary School in his Islington constituency in north London.
Asked if he was feeing confident, Corbyn smiled and said: "Extremely, it's a very good day."
On the outcome of the referendum, he joked: "You could either check the wind or check the bookies," adding "the bookies usually get it right".
Corbyn acknowledged that the odds on his election as party leader last year had not been favourable, grinning as he said: "I cost them (bookies) a lot of money."
The referendum has seen one of the longest, and most personally bitter, campaigns in recent British political memory.
Both sides of the campaign have been locked in fierce fighting for months, and things came to a frenetic close on Wednesday as senior politicians criss-crossed across the country to try to sway undecided voters.
The Prime Minister and his Remain colleagues from across the political spectrum have warned of the potentially severe economic consequences of a Brexit vote amid fears of financial market turmoil and another recession.
But Leave campaigners, led by Tory heavyweight Boris Johnson, have urged voters to "take back control" of the country.
They believe a divorce from Brussels would give the UK more money to spend on national issues like funding the NHS as well as giving the Government the ability to control the nation's borders and levels of immigration.
The campaign has been punctuated by ill-tempered exchanges and interventions, with both sides accusing the other of scaremongering, particularly over the issues of the economy and immigration.
Farage would not elaborate on his reasons for missing last night's final Channel 4 debate of the campaign, saying only that it was "for family reasons".
He came in for particularly stern criticism after unveiling a Brexit poster showing a queue of hundreds of immigrants arriving in Europe with the slogan "breaking point".
And Leave campaigners were left furious after Chancellor George Osborne made use of Treasury research to warn that quitting the EU would result in households being £4,300 a year worse off.
Meanwhile, dozens of celebrities have intervened during the course of the campaign to make their feelings known.
Footballer David Beckham, James Bond actor Daniel Craig and Harry Potter author JK Rowling were just three of the high-profile names to back the Remain campaign, while Leave won support from the likes of comedian John Cleese, former cricketer Sir Ian Botham and former England football player Sol Campbell.
The polls in the run-up to the big day have suggested the referendum result is on a knife-edge, with neither side able to surge ahead in the final weeks.
A record number of voters are eligible to take part in the referendum, with the Electoral Commission putting the number at 46,499,537.
Polling stations will close at 10pm.