Prime Minister Boris Johnson's ruling party appeared on course for a sweeping victory in Thursday's snap election, an exit poll showed, paving the way for Britain to leave the EU next month after years of political deadlock.

The Conservatives were forecast to win a thumping 368 out of 650 seats in parliament -- which if confirmed would be the party's biggest majority in three decades -- according to the survey published as polls closed.

UK general elections
British parliament has been deadlocked since the 2016 referendum on EU membership that saw a majority vote to leave. Photo: AFP / Tolga Akmen

The pound jumped by about two percent against the dollar on the projected results of what all sides had painted as the most momentous election in Britain in a generation.

Johnson had campaigned relentlessly on the promise to "Get Brexit Done", vowing to end years of political turmoil over Britain's future that has weighed on the economy and sharply divided the nation.

With a large majority of MPs, he will be able to get the divorce deal he struck with Brussels through parliament in time to meet the next Brexit deadline of January 31.

UK general elections
On the eve of a snap general election in the UK, British people hope it will help the country get out of Brexit uncertainty, but would also like to see other issues adressed such as homelessness and climate change. Photo: AFPTV / Mathilde BELLENGER

Ratifying the Brexit deal would formalise the end of almost five decades of EU-UK integration, although both sides still need to thrash out a new trade and security agreement.

EU leaders meeting in Brussels for a summit were watching the result closely, where France's European affairs minister, Amelie de Montchalin, was first to welcome the result.

UK general elections
Results of the 2016 Brexit referendum (by region) and the 2017 UK general election. Photo: AFP / Christopher HUFFAKER

"If the exit poll results are confirmed it should allow for a clear majority, something that has been missing in the United Kingdom for several years," she said.

UK general elections
Johnson needs just nine more seats for his party to secure a majority in parliament. Photo: POOL / Ben STANSALL

Britons had braved winter storms and howling winds as they lined up to cast ballots in Britain's third election in nearly five years.

Johnson's victory, if confirmed by official results, would be the best result for the Conservatives since 1987, when Margaret Thatcher was in Downing Street.

UK Brexit vote
Factfile on major parties participating in the British elections on December 12. Photo: AFP / Laurence SAUBADU

He tweeted his thanks to everyone who voted and supported his party, adding: "We live in the greatest democracy in the world."

By contrast, the exit poll spells disaster for the main opposition Labour party which was projected to win just 191 seats -- its worst result since 1935.

Left-wing leader Jeremy Corbyn had promised a second referendum on Brexit, in a bid to appeal to half of British voters who still want to stay in the EU.

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Labour leader Jeremy Corbyn has said he would hold a second referendum if elected. Photo: AFP / DANIEL LEAL-OLIVAS

But he had focused Labour's campaign on a radical programme of economic change, including nationalising key industries, which failed to woo traditional voters.

"It looks as if Brexit dominated. A lot of this was Brexit fatigue. People just wanted it over and done with," conceded his close aide, John McDonnell.

Corbyn was also personally deeply unpopular and dogged by accusations of sympathising with proscribed terror groups and failing to tackle anti-Semitism within the Labour party.

"We knew he was incapable of leading. He's worse than useless," said former Labour interior minister Alan Johnson.

If confirmed, it will be Labour's fourth successive electoral defeat -- and the second under Corbyn -- which could see the party out of power until 2024.

The anti-Brexit Liberal Democrats were also heading for a disappointing night, forecast to win just 13 seats, one more than they won in the election two years ago.

They performed well in European Parliament elections earlier this year, but new leader Jo Swinson failed to make an impact and experts suggest her promise to reverse Brexit without even a new referendum was unpopular.

Hopes also appeared to be dashed that "Remainers" would vote tactically to secure a second referendum.

By contrast the Scottish National Party (SNP), which wants to stop Brexit and deliver an independent Scotland, was forecast to win 55 of 59 seats available.

Former Scottish Conservative leader Ruth Davidson had pledged to swim naked in Loch Ness on New Year's Eve if the nationalists won 50 seats.

Johnson remains a polarising figure in Britain thanks to his leading role in the 2016 EU referendum vote for Brexit, which was marked by anti-immigration, populist rhetoric.

But he has again proved his ability to appeal across political lines, as he did when he was mayor of London -- aided by a simple message on Brexit.

Eurosceptic leader Nigel Farage also claimed to have boosted the prime minister's chances by declining to stand candidates for his Brexit Party in Tory-held seats.

The Brexit Party, like its former incarnation UKIP, is not predicted to win any seats.

He has then just 11 months to agree a new partnership with the EU before a post-Brexit transition period ends in December 2020.

UK elections
Polls open across London as general election begins. Photo: AFPTV / Fayruz RAJPAR

But with a comfortable majority in parliament, analysts note he could choose to extend that time and negotiate a closer trade deal than previously envisaged.

"Ironically, this is a freer hand for Johnson to negotiate a softer version of Brexit," said Simon Hix of the London School of Economics.

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