LONDON — Clearly anxious about her thin majority in Parliament before complicated negotiations on the British exit from the European Union, Prime Minister Theresa May on Tuesday called for a snap election for June 8, a vote that her opponents will bill as a verdict on her tough brand of “Brexit.”
In breaking her often-repeated vow not to call an early election before 2020, Mrs. May emphasized the need for unity in Parliament before undertaking what promises to be complex and tortuous negotiations on Britain’s exit from the bloc.
“The country is coming together, but Westminster is not,” Mrs. May said in a sudden appearance outside the prime minister’s residence at 10 Downing Street, adding that she had “only recently and reluctantly come to this conclusion.”
Having fired the starting gun for two years of talks with Brussels and the other 27 members of the European Union only last month, Mrs. May is already facing divisions within her own Conservative Party. She is clearly counting on a strong performance in June — before those talks get serious and difficult, before the British economy is seen to be hit and before critical German elections in the fall — to carry her government through the exit, hard or soft, which she has promised to deliver.
The financial markets bid up the pound on the news, apparently anticipating a Conservative sweep that would give Mrs. May the mandate to override hard-liners in her own party who might resist concessions to the European Union in return for market access — the so-called soft Brexit.
Certainly, the Conservatives’ election prospects look promising. They are riding high in the opinion polls, with the Labour Party under Jeremy Corbyn in disarray, the centrist Liberal Democrats weak and the shambolic far-right U.K. Independence Party, if anything, more a threat to Labour than to the Tories.
Although the margins are sure to tighten, the Conservatives hold a double-digit lead over Labour, which, if it holds up, would translate into a working majority in Parliament of over 100 seats, compared with only 17 seats now.
But the decision does carry political risks for Mrs. May. For a politician who has cultivated a reputation as a straight shooter who puts country before party, the about-face on early elections could smack of opportunism. And in a year of election surprises, embittered but highly motivated voters from the Remain camp could coalesce behind one of the parties to register their anger over leaving the bloc.
“She presents herself as someone putting the national interest first, before her party, and someone who does not play political games,” said Steven Fielding, a professor of political history at the University of Nottingham. “It might bite her, but she’ll play the stability versus instability card.”
But Mrs. May apparently calculated that the risks of an early vote were small compared with the possible payoff from a strengthened Conservative hold over Parliament.
Mrs. May took office less than a year ago, when David Cameron quit after losing the June 23 referendum on British membership in the European Union. Chosen by her Conservative Party to become prime minister when her most obvious rivals fell away, Mrs. May is now seeking an electoral mandate of her own to deal with her real danger: an unhappy group of anti-European Conservative legislators who are opposed to anything that might smell of compromise with the European Union.
Without an early vote, Mrs. May said, “the negotiations with the European Union will reach their most difficult stage in the run-up to the next scheduled election,” in 2020. She added, “Division in Westminster will risk our ability to make a success of Brexit and it will cause damaging uncertainty and instability to the country.”
Analysts generally praised her decision to call early elections. “This is the act of a rational politician, but one who had repeatedly promised not to call an early election,” Mr. Fielding said. “But her lead in the polls can only go down as soon as Brexit negotiations start, so why not go now?”
Some were more effusive, all but guaranteeing a Conservative sweep. “It’s a surefire certainty it will be a thumping majority, no doubt about it,” said Tim Bale, professor of politics at Queen Mary, University of London. “Something terrible about Theresa May would have to emerge between now and polling day for that not to be the case.”
The last election was only in 2015, when Mr. Cameron won a surprising but thin majority as the Labour Party lost heavily in Scotland and the Liberal Democrats were reduced to just eight seats in Parliament.
Labour’s choice of Mr. Corbyn, a man of the hard left, has proved hugely unpopular, but on Tuesday he issued a statement welcoming an early election, as politically he had to do. That makes it likely that Parliament on Wednesday will give Mrs. May the two-thirds majority she needs to call an early election under the Fixed-Term Parliament Act, which otherwise mandates an election in May 2020.
“I welcome the prime minister’s decision to give the British people the chance to vote for a government that will put the interests of the majority first,” Mr. Corbyn said in a statement. “Labour will be offering the country an effective alternative to a government that has failed to rebuild the economy, delivered falling living standards and damaging cuts to our schools and N.H.S.,” the National Health Service.
Mr. Corbyn, 67, was elected after Labour’s bad defeat in 2015 and took the party strongly to the left. He was a weak supporter of the Remain campaign, and efforts by Labour legislators to unseat him have failed. He will lead a badly divided party and, should Labour lose this election, too, as expected, will be under considerable pressure to resign.
The Liberal Democrats, under a new leader, Tim Farron, have been explicitly against leaving the bloc and have called for another referendum on any final deal with Brussels. Though the Liberal Democrats are expected to win back some seats in June from the Conservatives, the Conservatives are expected to win more seats from Mr. Corbyn’s Labour Party, in that many Labour constituencies in Britain’s hard-pressed northern cities voted strongly for leaving.
While a third or so of Conservative voters voted against leaving, they are considered likely to back Mrs. May, given the alternatives, especially as she has hinted lately that a transitional deal with Brussels would most likely involve some compromises in the national interest.
Mrs. May portrayed the election as one of leadership. “It will be a choice between strong and stable leadership in the national interest, with me as your prime minister, or weak and unstable coalition government, led by Jeremy Corbyn, propped up by the Liberal Democrats who want to reopen the divisions of the referendum,” she said on Tuesday.
The Liberal Democrats have promised to bludgeon the Conservatives with the specter of a “hard Brexit,” in which Britain would leave the European Union’s single market and customs union without a mitigating trade agreement.
On Tuesday, Mr. Farron said that “if you want to avoid a disastrous hard Brexit, if you want to keep Britain in the single market, if you want a Britain that is open, tolerant and united, this is your chance.”
“Only the Liberal Democrats can prevent a Conservative majority,” he added.
Mr. Cameron also endorsed Mrs. May’s announcement, calling it a “brave — and right — decision.”
The leader of Scotland, Nicola Sturgeon of the Scottish National Party, was harsh, saying, “This announcement is one of the most extraordinary U-turns in recent political history, and it shows that Theresa May is once again putting the interests of her party ahead of those of the country.”
Ms. Sturgeon, who favors an independent Scotland but also wants to remain within the European Union’s single market, said the snap election was about “standing up for Scotland in the face of a right-wing, austerity-obsessed Tory government with no mandate in Scotland but which now thinks it can do whatever it wants and get away with it.”
Paradoxically, however, a more confident Mrs. May, with a larger majority, is likely to be able to negotiate more flexibly with Ms. Sturgeon over final terms to leave the bloc and undercut momentum for another Scottish independence referendum.
In recent weeks, Mrs. May’s office had repeatedly insisted that an early election was not going to happen, despite considerable pressure to call one from party notables like the former leader William Hague. But British politicians remember well how speculation that a former Labour prime minister, Gordon Brown, was to call an early election in 2007 rebounded on him when he failed to follow through, destroying his credibility.
Mr. Brown took office after his predecessor, Tony Blair, stepped aside. Despite polls showing that Labour would win a commanding majority and provide him his own mandate, Mr. Brown waited and suffered from the 2008-9 financial crisis, despite his skillful management of it, and Labour lost the 2010 election.