London: Britain has gone to the polls, at the end of a surprise election campaign that featured two terror attacks and a Labour surge, but was predicted to end with a return to power for Theresa May's Conservatives.

Polling stations were to close at 10pm in Britain (7am Friday on Australia's east coast), at which point an exit poll would be published that could inspire immediate celebrations from the Tories, but just might lead to a long night of counting before the final result is certain.

Security was stepped up at some of the schools, community centres and parish halls where the UK's 47 million registered voters could cast their ballots, following recent terror attacks in Westminster, Manchester and London Bridge.

Plans were reviewed after the two most recent attacks. Armed police were on patrol in some areas. 

Lucy D'Orsi, the National Police Chiefs Council lead for protective security, said: "Security around polling stations is constantly being reviewed and updated by local police forces.

"Plans are in place to make sure that resources are appropriately allocated. The general threat level remains at severe, so we continue to ask the public to be alert and to report any concerns to police."

A severe threat level means a terror attack is 'likely' but not considered imminent.

The rival would-be prime ministers returned to their core messages on the frantic final day of campaigning.

"No-one can say there wasn't a choice," Labour's Jeremy Corbyn said, warning that a Conservative victory would mean five more years of Tory cuts, longer waiting lists and underfunded schools, compared with "hope under Labour".

At his 90th and final campaign rally in his home constituency of Islington he said Labour had "changed the debate and given people hope" and presented "the policies that people actually want".

"Inequality can and will be tackled," he said. "Austerity can be ended, we can stand up to the elites and the cynics."

Brexit matters, Brexit is the basis of everything else.

Theresa May

"This is the new mainstream."

Meanwhile, Theresa May toured marginal Labour seats that her Conservative Party hopes to pick up by promising the best Brexit deal for Britain.

The Tories have aggressively courted former Labour voters who left for the UK Independence Party, and even the Labour faithful who voted for Leave in the 2016 Brexit referendum.

"Brexit matters, Brexit is the basis of everything else," Mrs May said on Wednesday, repeating her campaign mantra of "strong and stable leadership".

"Give me your backing and I will deliver for Britain," she said.

Polls this week have ranged from predicting a minority Labour government, through to a big majority for the Conservatives.

In the final polls, the Conservatives' lead ranged from just one point (Survation), through seven points (Opinium), 10 points (ComRes) up to 12 points (ICM).

YouGov, which last week projected a Labour minority government, found a last-minute Tory surge in its final poll and gave them a seven-point lead and an increased majority.

Even if Labour gets a lower vote share than the Conservatives, if it picks up enough seats it might still form a government with the backing of the Scottish National Party and the Liberal Democrats.

But Labour insiders are privately predicting a net loss of seats, and devoted the last days of the campaign to shoring up Labour-held seats rather than pushing into Conservative territory.

Mr Corbyn has drawn huge crowds to rallies around the country, in an energetic last push for votes – while May has settled for smaller, more contained events in front of core supporters and TV cameras.

Writer Robert Harris recalled covering the 1983 election when Margaret Thatcher ran "a new kind of election, an American-style copied from Reagan where you didn't do the monster rally, you just got good pictures for the evening news". Meanwhile, Michael Foot fronted huge rallies around the country – and lost.

The nation's leading tabloids have come out strongly in favour of May – as expected – with the Daily Mail devoting the first 13 pages of its Wednesday paper to attacking Mr Corbyn and his colleagues who they called "apologists for terror".

The Sun led with 'Jezza's jihadi comrades", referring to a 2002 speech he gave at Trafalgar Square that was attended by followers of hate preachers linked to the London Bridge attackers.

On Thursday The Sun's front page pleaded "Don't chuck Britain in the Cor-bin", describing Corbyn as "terrorists' friends, useless on Brexit, destroyer of jobs … Marxist extremist".

Corbyn supporters responded to the barrage on Wednesday with a humorous series of tweets on the topic of "last minute Corbyn smears", warning that the Labour leader would give dogs a vote, and had used steroids to grow an enormous marrow on his allotment.

The Financial Times said a Tory vote was a "safer bet" and the Times said the campaign had exposed May's flaws but a cabinet led by Mr Corbyn would be "a catastrophe".

Of the daily newspapers only three came out for Mr Corbyn. The Mirror said Labour would deliver a "fairer, decent, prosperous, better land" and The Guardian that Mr Corbyn's party "might be the start of something big rather than the last gasp of something small".

The avowedly communist Morning Star said approvingly that Mr Corbyn "has put socialism back on the political agenda".

Late in the campaign attention turned to Scotland, where the Conservatives are a good chance to pick up a handful of seats from the Scottish National Party (SNP) which won almost the entire country in 2015.

SNP leader Nicola Sturgeon said Mrs May would be regretting calling this "unnecessary election", and had thought she could cruise to victory just by repeating "strong and stable".

Ms Sturgeon used the final day of campaigning to issue a plea for Labour and Liberal Democrat supporters to lend the SNP their votes.

A vote for Labour or the Lib Dems risked "allowing the Tories in the back door", she said.

Britain has a first-past-the-post voting system.

She said they might disagree over SNP policies – such as their push for another Scottish independence referendum – but "if you do not want to wake up tomorrow morning with a Tory government with a bigger majority, vote SNP".

The last week of the campaign has been overshadowed by security issues, following the attack in London Bridge – and Manchester before that.

But Brexit has been the most popular policy issue in Britain's general election on Twitter, eclipsing even the NHS, according to new research from the University of Edinburgh's Professor Laura Cram.

Wednesday saw a lighter moment on the election trail, as Foreign Secretary Boris Johnson asked a gypsy fortune teller in Plymouth in the south-west for her election prediction, and she refused.

"You're having a laugh, you're taking away my pension and my rights and then you come and ask me for something for nothing."

Her husband insisted it would be Labour.