The Conservatives are set to win an overall majority of 86 in the general election, according to an exit poll for the BBC, ITV and Sky News.
The survey taken at UK polling stations suggests the Tories will get 368 MPs – 50 more than at the 2017 election – when all the results have been counted.
Labour would get 191, the Lib Dems 13, the Brexit Party none and the SNP 55.
In the exit poll, voters are asked to fill in a mock ballot paper as they leave the polling station indicating how they have just voted.
The exit poll was conducted by Ipsos Mori at 144 polling stations, with 22,790 interviews.
Exit polls have proved to be very accurate in recent years. In 2017 it correctly predicted a hung Parliament, with no overall winner, and in 2015 it predicted the Conservatives would be the largest party.
The pound surged against the dollar after the exit poll figures were announced, with sterling gaining 3% to $1.35 – its highest level since May last year. The pound also jumped to a three-and-a-half-year high against the euro.
If the exit poll is correct, and Boris Johnson has secured a majority, then he will have the backing of MPs on the green benches behind him to take us out of the European Union next month.
A huge junction in our history – a moment that will redraw our place in the world.
But not just that – if correct, these numbers could mean five more years of a Conservative government – tipping across a decade.
After the fourth defeat for Labour in a row – after several years when they have moved further to the left – this is a serious and historic loss.
The SNP have increased their dominance in Scotland, clearing out Conservatives there in a way that leaves most of the country yellow, rather than blue.
And it is a failure for the Lib Dems to break through after a campaign that started with high hopes.
It would be the biggest Conservative victory since 1987 and Labour’s worst result since 1935, the poll suggests, with the party forecast to lose 71 seats.
The exit poll suggests the parties’ shares of the vote reflected differences in how constituencies voted in the 2016 EU referendum.
It suggests the Tory strategy of targeting Leave-voting Labour seats in the Midlands and North of England might have paid off, with Boris Johnson’s party expected to have made gains at the expense of Labour.
In contrast, the Conservative share of the vote is expected to fall back on the 2017 general election in those areas that voted most strongly for Remain in the 2016 EU referendum, while Labour’s vote is expected to fall back rather less, according to polling expert Sir John Curtice.
As a result, the Conservative share of the vote is expected to be slightly lower in London and Scotland and do little more than replicate the 2017 result in the South East outside of London.
But it will not become clear whether the exit poll is accurate until the results start rolling in during the early hours of Friday.
Home Secretary Priti Patel said the government will move quickly to “get Brexit done” before Christmas by introducing legislation in Parliament, if it is returned to power.
Shadow chancellor John McDonnell told the BBC the exit poll was “extremely disappointing” for Labour if it was correct.
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“I thought it would be closer. I think most people thought the polls were narrowing,” he added.
Mr McDonnell said the election had been dominated by Brexit and Labour had been hoping “other issues could cut through”.
He told the BBC’s Andrew Neil decisions would be made about party leader Jeremy Corbyn’s future when the actual results were in.
‘Get Brexit done’
This is the UK’s third general election in less than five years – and the first one to take place in December in nearly 100 years – and has been dominated by Britain’s 2016 vote to leave the European Union.
Mr Johnson focused relentlessly on a single message – “get Brexit done” – promising to take the UK out of the EU by 31 January 2020 if he got a majority.
His main rival for No 10, Labour leader Jeremy Corbyn, promised voters another referendum with a choice between a renegotiated Leave deal and remaining in the bloc.
But Labour primarily campaigned on a promise to end austerity by increasing spending on public services and the National Health Service.
The Liberal Democrats promised to cancel Brexit if leader Jo Swinson became prime minister, but opinion polls suggested their vote was squeezed during the course of the campaign.
The Lib Dems did a deal with the Green Party and Plaid Cymru to stand aside in certain seats to maximise the pro-EU Remain vote.
The Scottish National Party said a strong vote for them would effectively be a mandate for a second independence referendum.
SNP leader Nicola Sturgeon tweeted that while the exit poll “suggests a good night” for the SNP, she added that “what it indicates UK-wide though is grim”.
The Green Party’s Caroline Lucas tweeted: “If this exit poll is right, it’s a devastating blow for our climate, for future generations and for our democracy.
“It’s not just our relationship with the EU that will dominate the next few months, it will be our relationship with Scotland too.”
A decisive moment came early on in the campaign when Nigel Farage announced his Brexit Party would not be standing in seats won by a Conservative at the 2017 general election to avoid splitting the Leave vote.
Mr Farage said his party had taken votes from Labour in Tory target seats, although he himself had spoiled his ballot paper “as I could not bring myself to vote Conservative”.
The Conservatives began the campaign with a double-digit lead over Labour in the opinion polls, although this narrowed as polling day approached.