LONDON — For the second time since Britain voted to withdraw from the European Union, and with the country still deeply divided over the outcome, voters will head to the polls on Thursday for a general election.
With the future of Britain’s status in Europe still undecided after years of haggling, Brexit has inevitably been high on the agenda, with Prime Minister Boris Johnson’s vow to “get Brexit done” at the core of his Conservative Party’s campaign.
But the opposition Labour Party, led by Jeremy Corbyn, has put health care at the center of its pitch to voters, framing itself as the defender of Britain’s revered National Health Service. Labour pledges to increase spending. It’s also arguing that Mr. Johnson could further privatize the service, or accept a trade deal with the United States that might lead to a steep increase in drug prices, claims that Mr. Johnson disputes.
With very different visions for the future of Britain laid out by the leaders of the country’s two main political parties, and several smaller parties also playing potentially decisive roles, here’s what to know ahead of the election.
Voters will be choosing a representative for their local district, or constituency, in Parliament. In total, 650 lawmakers — one for each district — will be chosen as members of the House of Commons, which decides the country’s laws and policies.
Any British citizen or citizen of the Commonwealth or Ireland who is 18 or over and lives in Britain could register to vote. (It’s too late now, though: The deadline was Nov. 26.) Elections are typically held every four or five years, but Parliament can vote to hold a new election whenever it wishes, and this will be the third since 2015.
The polls open at 7 a.m. local time and close at 10 p.m., with the results of a usually reliable exit poll announced almost immediately after that. For the official results, all the ballot papers are counted by hand — some districts manage to declare a winner barely an hour after polls close, but most do so overnight.
While the Conservative and Labour parties are Britain’s largest, several smaller parties are running candidates.
If one party wins more than half of the parliamentary seats, it will form the government, and its leader will become the prime minister.
For decades, such majority governments were by far the most common result. But that has happened only once in the past three elections. The other two produced “hung Parliaments,” with no party strong enough to govern on its own.
In that case, the largest party usually has the first chance to assemble a parliamentary majority and form a government.
It can do so by agreeing to a formal coalition with one or more smaller parties and governing on a joint program, as the Conservatives did with the centrist Liberal Democrats after the 2010 election.
Or it can form a minority government, and seek a looser deal for smaller-party support on critical votes — known as a “confidence and supply” arrangement. The Conservatives struck one of these with a Northern Ireland party, the Democratic Unionists, after the 2017 election.
When the results are known — and if a party clearly comes out on top — the head of that party visits Buckingham Palace to ask the queen for permission to form a new government and become the prime minister.
Britons do not vote directly on the prime minister but rather on a politician to represent their district, or constituency. Unlike the proportional systems used in several other European countries, where seats are apportioned according to the share each party receives of the overall vote, British elections are “first past the post”: Each voter has one vote, and the single candidate who gets the most votes in each constituency wins.
That means the winning candidate in any given constituency doesn’t need a majority of the votes, just more than the next person. And votes for a party nationwide don’t necessarily translate into seats: What counts is how many constituencies a party comes first in.
It’s a system both praised and criticized for its ability to turn a plurality of the votes into a single-party government with a majority of parliamentary seats — sometimes, when opposition votes are badly split, a landslide majority.
When Prime Minister Theresa May called a surprise early general election in 2017, the opinion polls gave her Conservative Party a lead of at least 20 percentage points on the Labour opposition. Mrs. May set out to expand the narrow parliamentary majority her party had won in 2015, to assure a smooth exit from the European Union.
But things didn’t go quite as planned.
Mrs. May suffered a humiliating setback, with her Conservative Party losing its overall majority and instead forced to rely on the 10 votes of the Democratic Unionist Party to retain control in a minority government.
The opposition Labour Party saw its support grow substantially, gaining 32 seats, driven in part by a spike in the youth vote.
The Conservative Party has established a clear but potentially narrowing lead over the Labour Party in national polls, with Labour appearing to consolidate its support as the country headed into the final stage of the campaign.
On Tuesday, a highly regarded prediction model run by the polling company YouGov suggested the Conservatives were on course for a majority of 28.
But analysts, including the ones behind that model, warn that predictions are perilous: 11 seats were decided by less than 100 votes at the last election, and dozens more by a few hundred votes, so a small shift in the right places could change the picture drastically.
A recent study from the U.K. Political Studies Association found experts confident that the Conservatives would remain the largest party, but more skeptical of the polling that suggests they will regain an outright majority.
“This cautious prediction of no majority or a very small majority for the Conservatives by the experts may reflect lessons learnt from 2017, when the hung parliament surprised many,” Joe Greenwood, a fellow at the London School of Economics, wrote of the study. “If the experts are right then 2019 may be a slightly less dramatic, but surprising nonetheless, rerun of 2017, and we are now only a matter of days from finding out.”
Tactical voting sees individuals cast a ballot for a candidate they wouldn’t normally support to block another candidate from winning.
It’s been a major discussion topic in this election campaign because Britain’s first-past-the-post electoral system presents a puzzle for voters who see Brexit as the most important issue.
Those seeking to remain in the European Union are split between several parties. Pro-remain groups have attempted to unite voters behind the most promising pro-European candidate in each constituency — in England, usually from Labour or the Liberal Democrats — amid furious disputes about who has the best chance in certain seats.