A protester wearing a Theresa May mask is seen the day after Britain's election in London, June 9, 2017.
A protester wearing a Theresa May mask is seen the day after Britain's election in London, June 9, 2017.

LONDON - Britain was thrown into political uncertainty Friday after Labour, the main opposition party, made an extraordinary electoral comeback, denying Prime Minister Theresa May and the ruling Conservatives a majority in the House of Commons, largely due to a surge in youth voters.

In what will rank as one of the most remarkable elections in modern British history, May's gamble to expand her party's parliamentary majority failed spectacularly, raising doubts that she will be able to lead a minority government with the support of Northern Ireland's Unionists.

Britain's Prime Minister Theresa May waits for the
Britain's Prime Minister Theresa May waits for the result of the vote in her constituency at the count center for the general election in Maidenhead, June 9, 2017.

Calls mounted from the Labour Party, the leaders of third parties and some Conservatives for the prime minister to step down.

The embattled prime minister announced from the steps of Downing Street after seeing the queen that she would start forming a government. The speech - with just a mention of the Unionists and the support they would provide her minority government - offered little recognition of the rebuff she had hours earlier received at the polls. It was a speech May could have given had she scored a big win.

"What the country needs more than ever is certainty," she said. May claimed that as the biggest party in the House of Commons, Conservatives could provide that certainty. May said she would form a government that will take Britain out of the EU. She said her government would crack down on Islamic extremism.

May will likely face a vote of confidence in the House of Commons next week.

Despite their anger at her decision to call a snap post-Brexit referendum election and her conduct of the party's campaign, Conservative lawmakers appeared ready in the short term to back her.

If May were to lose the Commons confidence vote, it would give Labour a chance to form a coalition of its own, or seek to govern as a minority government, although it is unclear if Labour would be able to do so.

Jeremy Corbyn, leader of Britain's opposition Labo
Jeremy Corbyn, leader of Britain's opposition Labour Party, arrives at the Labour Party's Headquarters in London, June 9, 2017.

?Calls for May to step down

Labour leader Jeremy Corbyn, who was all but written off at the start of the election campaign seven weeks ago, called on the prime minister to resign, saying she should "go and make way for a government that is truly representative of this country." He said Labour had denied her a hard Brexit' mandate.

"We are ready to do everything we can to put our program into operation," he added.

Former Conservative finance minister George Osborne, removed from the Cabinet by May and now editor of the Evening Standard newspaper, told ITV, "I doubt she will survive in the long term as Conservative party leader."

Former Conservative minister Anna Soubry said May should take responsibility for a "dreadful" campaign.

Among Conservatives there was clear fury at the result, a seismic political shock that could trigger a second election within months. Few commentators appeared to believe that a minority Conservative government is sustainable for more than a few months. "Does she really think she can blunder on?" said Lord Ashcroft, a former Liberal Democrat leader.

Supporters watch Jeremy Corbyn the leader of Brita
Supporters watch Jeremy Corbyn the leader of Britain's opposition Labour Party, as he speaks at an election campaign event in Harrow, June 7, 2017.

?Brexit not the only issue

Exit polls late Thursday, suggesting Britain was heading for a hung parliament, prompted gasps at Conservative Party headquarters in London.

May focused her party's election campaign on Brexit, saying she would be able to bring the strength necessary to get the best deal for Britain with the European Union.

At the start of the campaign it looked as if she might pull off a landslide victory, but opinion polls showed the race tightening, and May came under criticism for running an aloof campaign that took voters for granted.

A turning point appeared to come when the parties unveiled their election manifestos. The Conservatives had to backtrack on plans to make the elderly pay more for residential and social care.

May spent more than half of the election campaign in Labour-held seats, demonstrating how confident she was of making gains from a Labour Party led by the most left-wing leader in its history, a man the press sees as a throwback to the militant 1970's.

With more than a week to go before Brexit negotiations, it remains unclear whether Britain will have a government in place to take on the formal talks — or whether the government that starts the talks will be the one that finalizes them.

European officials and lawmakers warn that a hung parliament could be a "disaster" that hugely increases the chance of Brexit talks failing. They said political uncertainty would likely delay talks, with Michel Barnier, the EU's chief negotiator, questioning whether he would have someone to really negotiate with about Brexit.

FILE - A journalist poses with a copy of the Brexi
A journalist poses with a copy of the Brexit Article 50 bill, introduced by the government to seek parliamentary approval to start the process of leaving the European Union, in front of the Houses of Parliament in London, Jan. 26, 2017.

Guy Verhofstadt, the European parliament's Brexit representative, described the result as "yet another own goal" for Britain.

Some analysts compared the political situation to 1923, when Conservative Stanley Baldwin failed to win a parliamentary majority, struggled on for a few months as prime minister and then lost a confidence vote in the House of Commons. The king then had to ask Labour to form a minority government.

The election result also throws into doubt whether Britain will now seek the hard Brexit that May and the right-wing of her party have been advocating. There is now likely a majority across the parties in the new House of Commons for a softer Brexit, one that might see Britain remain in the single market.

"What it means is we will have pressure in the House of Commons for a soft Brexit," said Jack Straw, a former Labour foreign minister. "The math and chemistry in the Commons will be pushing away from a hard Brexit," he added.

Nigel Farage waits for the start of a debate on th
Nigel Farage waits for the start of a debate on the last European Summit at the European Parliament in Strasbourg, France, Oct. 26, 2016.

Leading Brexit campaigner Nigel Farage complained about the election result in a tweet, saying May's failure had put Brexit in jeopardy. Some commentators argued the election could be seen as a second referendum on Brexit, a vote about a hard' or soft Brexit,' certainly when it came to the youth vote.

Hundreds of thousands of people ages 18 to 34 registered to vote before last month's closing date, including more than 450,000 on the final day. Voters ages 18 to 24 appear to have voted heavily in favor of Labour.