Brexit has turned traditional political allegiances on their head and shock results could be on the cards, with tactical voting expected along Leave/Remain, rather than party lines.
Prime Minister Boris Johnson and Labour Party leader Jeremy Corbyn have travelled the country in the run-up to the vote, with the Conservatives in the lead and Labour hoping to attract enough support to pursue a second referendum on European Union membership. He said Friday he would not lead the party into another election, but would stay on during a "process of reflection".
It could also result in the complete opposite. AP's earlier story follows below.
But a win for the opposition, or a hung parliament, could still reverse Brexit and give Britain a hard-left government headed by Labour party leader Jeremy Corbyn - a veteran socialist committed to renationalisation and massive public sector spending.
It would also make Johnson the most electorally successful Conservative leader since Margaret Thatcher, another politician who was loved and loathed in nearly equal measure.
Scottish Labour leader Richard Leonard has described results for his party as "deeply disappointing".
Jeremy Corbyn's Labour Party is forecast to pick up 191 seats - down 71. Projections show them sitting at 368 of the 650 seats, a 50-seat bump from the 2017 elections.
It would be the biggest Tory majority since Thatcher's 1980s' heyday, and Labour's lowest number of seats since 1935.
Corbyn's hopes of heading the government would depend on support from the pro-EU Scottish National Party (SNP) and the Liberal Democrats.
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In a statement released by the party, it was confirmed that Ed Davey and Sal Brinton would take over as joint interim leaders. She led the party into the General Election with a pro-remain message, but it wasn't enough to secure a strong backing.
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Pound rockets as Boris Johnson's Conservatives win general election 2019
Results poured in early Friday showing a substantial shift in support to the Conservatives from Labour . Labour leader Jeremy Corbyn poses outside the polling station at Pakeman Primary School, Holloway.
In a symbol of Labour's failure, Blair's old parliamentary seat of Sedgefield fell to the Conservatives.
Corbyn said the Conservatives were the party of "billionaires" while Labour represented the many.
A decisive Conservative win would vindicate Johnson's decision to press for Thursday's early election, which was held almost two years ahead of schedule.
The exit poll suggests Johnson's strategy had breached Labour's so-called "Red Wall" of seats across the Brexit-supporting areas of the Midlands and northern England where he cast his political foes as the out-of-touch enemies of Brexit.
Johnson has warned that every vote for the Brexit Party on Thursday will increase the likelihood of Labour gaining power after a new analysis revealed that Nigel Farage, leader of the Brexit Party, could stop the Tories taking 16 seats.
"I wasn't happy. Brexit should not be dominating", voter Gaurang Naik said. "We thought other issues could cut through and there would be a wider debate, from this evidence there clearly wasn't".
Polls are open in the United Kingdom, as voters make an important choice.
The party faces a brutal internal battle between Corbyn's followers and his critics, who want the party to return to the centre ground it occupied under former prime minister Tony Blair. "We live in the greatest democracy in the world".
Yet the complex process of unwinding ties between the single market of 27 remaining European Union nations and the bloc's second-biggest economy would run on long after the first stage of Brexit ends next month.