In short:
An exit poll is predicting voters in the UK have elected a Labour government.
The Conservative Party had held power for 14 years.
What's next?
The actual polls have closed and vote counting has begun, although the final results will not be known for a couple more hours.
Britain's ruling Conservative Party appears set to be thrown out of government after 14 years, with an exit poll released as the polls closed predicting it will cop an historic election defeat.
While the official results in the United Kingdom's snap general election are still being counted, the poll is considered the best possible crystal ball until all the actual votes are counted.
It showed the opposition Labour Party, led by Sir Keir Starmer, on track to win at least 410 of the country's 650 lower-house constituencies. To form government, a party must win 326 seats.
The poll predicted that the Conservatives — also known as the Tories — would win just 131 seats, which is their lowest total ever. They had gone in to the election with 345.
Conservative minister Dominic Grieve didn't hold back when describing the predicted landslide loss, telling the ABC that it was a "sad day" for the party and "perhaps one of the worst in its history".
The sample, gathered as voters left 133 polling stations around the country after casting their actual ballots, is widely regarded as the most reliable indicator available until the final results are declared.
If the poll is right, it means Sir Keir will replace Rishi Sunak as Britain's prime minister.
The Labour leader arrived at his seat's counting centre in Kings Cross, central London with a broad grin on his face about 2:30am Friday morning (11:30am AEST).
As results began coming in, it was clear Labour was taking dozens of seats off the Conservatives, who were also bleeding votes to the right-wing Reform UK party.
Conservative minister Steve Baker told the BBC the predicted result represented an "extremely difficult moment" for the party.
"We've just had a torrid time, a dreadful result, there will be, undoubtedly, recriminations," he said.
Labour's Rachel Reeves, who will be in the cabinet if the party forms government, told the broadcaster Sir Keir was determined to "bring growth back to Britain".
"This an almost unprecedented landslide majority," she said.
"This will give us a mandate to make the changes that the country needs."
The predicted Tory rout is not considered surprising. Over the course of the campaign, multiple polls have all said the same thing: Labour would win in a landslide.
Indeed, the party has been ahead of the Tories in every sample taken since the start of 2022.
A YouGov poll published on Wednesday was so dire for the Conservatives, it said there was a chance the centerist Liberal Democrats, who currently have 11 MPs, could win enough to become the second largest party in the parliament and therefore the official opposition.
Labour has promised to revitalise Britain's public health system and grow the country's stuttering economy if elected.
Meanwhile, the Conservatives spent significant time ahead of the election focusing on immigration policy.
Sir Keir has said he would scrap the government's plans to deport some asylum seekers who arrived in the UK to Rwanda if Labour was elected.
The Conservatives first squeaked into office in 2010 after forming a coalition with the Lib Dems, won a majority in 2015, then governed in minority after a snap 2017 election. But in 2019, Boris Johnson led them to a commanding victory.
Their 14 years in government have been among the most tumultuous in British history, and included the country voting to leave the European union, the COVID-19 pandemic and multiple political scandals.
The exit poll released at 7am on Friday AEST, also predicted significant changes among the UK's smaller parties.
The Lib Dems were predicted to become the country's third-largest party, with 61 seats (up from 13), while the far-right Reform UK could pick up as many as 13 seats.
Ahead of the election, multiple polls pointed to Reform, led by high-profile populist Nigel Farage, taking a hammer to the Conservatives vote.
Health Minister Dame Andrea Leadsom told the BBC that, according to the exit poll, it appeared Reform had done "vast damage" to the Conservatives.
Meanwhile, high-profile Tory MP Jacob Rees-Mogg told the BBC the party had taken its "core vote" for granted.
"That was always a problem. Our base was peeling off to Reform," he said.
Lee Anderson, a former Conservative MP who defected to Reform, retained the seat of Ashfield just after 2am, local time, becoming the party's first candidate to win a constituency at a general election.
"This wonderful place that I call my home is going to have a massive say in the future of this country," he said. "I want my country back."
The Scottish National Party, which had held 48 seats, was expected to have its number of MPs slashed to 10.
There are several major differences between the way elections are staged in the UK, compared to Australia.
Early voting is not available in Britain, but people are given longer to cast their ballot on election day with polls open from 7am to 10pm local time.
Voting also takes place on a weekday, and instead of preferential voting (like Australia), Britain uses a first-past-the-post system, which means the candidate with the highest number of ballots wins.
Liberal Democrat MP Daisy Cooper told the BBC Britain's first-past-the-post system was broken, but agreed that her party had learnt how to "play the game" better.
"We've been clear now for many years that our goal is to unseat as many Conservative MPs as possible," she said.
Voting is also not compulsory in the UK, and the country's upper house — called the House of Lords — is completely unelected.