Conservative party leader May and Labour chief Corbyn were among the early voters as they cast their votes at the end of a frenetic 50-day campaign that suffered breaks due to terrorist strikes in Manchester and London.
May was joined by husband Philip at her Maidenhead constituency in south-east England, while Labour party's Corbyn cast his ballot at Holloway in London -- the two main choices before the electorate to take over as the new Prime Minister after the snap poll announced on April 18.
May is on course to increase her majority in the House of Commons with a final General Election 2017 poll giving the Tories a lead of eight points over Labour as the nation headed to the ballot box, British media reported.
The Conservatives had as much as a 24 point lead when the snap election was called by the Prime Minister.
Ipsos MORI's final 2017 election survey for the Evening Standard, which was undertaken on Tuesday and Wednesday this week, put the Conservatives on 44 per cent and Labour on 36.
To form a majority in the House of Commons, one party must win 326 seats.
May, 60, called the election three years earlier than scheduled ahead of what are expected to be tough negotiations with the European Union over Britain's exit from the 28- member-bloc -- Brexit.
Britain last voted in a general election in 2015, when then Prime Minister David Cameron won a majority with 331 MPs for the Conservative party. Since then the referendum on Britain's membership of the European Union (EU) in June 2016 has meant a very different political landscape.
The ongoing voting is the fourth major UK poll in three years, following the 2014 Scottish independence referendum, the 2015 general election, and the 2016 Brexit vote.
Police have increased security at polling stations, including patrols by armed officers in some areas, following the recent terror attacks.
A spokesperson for the UK's National Counter Terrorism Policing Headquarters has said security around polling stations was being "constantly reviewed and updated by local police forces".
"Every London borough will have a specific, dedicated policing operation. Across London there will be a specialist and highly flexible operation in place that can deploy and respond as needed," a Scotland Yard statement said.
Political parties had called a halt to campaigning both times but May had said that terrorism must not be allowed to derail the democratic process.
May decided to overturn the UK's Fixed Term Parliament Act, which would have seen an election being held after a fixed five-year term in 2020 and called a snap general election back in April with the aim of winning a strong mandate for Brexit negotiations.
The shape the new government is likely to take is expected to emerge after midnight,with a steady trickle of results until about 2 AM (local time) when declarations should start to come in from across the UK.
The main wave of results is expected to start at about 3 AM (local time) with the overall picture likely to be clear by about 5 AM (local time) tomorrow.
The leader of the winning party traditionally waits for the leader of the losing party to concede defeat before claiming victory.
Many of the votes have already been cast through postal voting, which accounted for 16.4 per cent of the total electorate at the 2015 general election.
Overall turnout in 2015 was 66.4 per cent, up from 2010.
Counting will begin immediately after the polls close, with each vote counted and checked by hand.
The pre-poll forecasts have also been echoed in the nearly 100 million pounds expected to be bet on the outcome of the polls.
Betfair, another leading bookmaker, also views the Tories as the odds-on favourite to win the general election, with odds of 1/12.
However, there are some pundits who point out that the pre-poll patterns are following similar trends as for the Brexit referendum vote in June 2016, the outcome of which had taken most pollsters by surprise.
The betting odds being offered for a hung Parliament have also narrowed after some recent opinion polls had indicated the possibility of such an outcome.
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