Meanwhile the Scottish National Party of First Minister Nicola Sturgeon, which has dominated politics north of the border for a decade and called for a new independence vote after Brexit, was tipped to lose around 21 of its 54 seats.
However parliament is due to meet again on Tuesday and if there is a clear sign that Mrs May can not form a government she will to resign.
From a position of relative strength, dominating a compliant parliament which had accepted Brexit, Theresa May is now struggling to cling on to her job, unsure whether she will even be able to form a government.
As she was resoundingly re-elected to her Maidenhead seat in southern England, May looked tense and did not spell out what she planned to do.
This would require her juggling to keep different factions of her party on side and leaves her at constant risk of alliance-building by opponents aimed at softening her plan.
"We know Theresa May can't now negotiate Brexit for Britain because she told us losing majority would destroy her authority - and it has", Miliband wrote on his official Twitter account. It is unlikely she would agree to stopping the Brexit divorce.
Delays or outright blockages on this legislation would place doubts over how Britain would control its borders and trade with the European Union after Brexit.
Negotiating teams and leaders from across the parties will now be in talks as they try to put together a coalition government.
2010 revisited: Conservative-led coalition? The other parties that could push a Conservative-led government over the line, like the Liberal Democrats, have pledged not to cooperate with the Tories. They governed together until 2015.
Not necessarily. A majority coalition is a formal agreement between two or more parties who between them have more than 323 MPs.
Conservative MP for Ribble Valley Nigel Evans summed up what was the story of the Tory election campaign, saying: "It was a Rolls-Royce at the beginning and a clapped-out Robin Reliant at the end". This limits their ability to take May's support above the require threshold.
MIT says Trump misused its research in ditching climate deal
After the announcement , a handful of states - including Hawaii , Washington and NY - pledged to uphold the treaty's goals. I am looking to you to help publicly support the U.S.'s commitment to The Paris Agreement on climate change.
The Conservatives' other coalition options are limited.
In the short-term, the only way that May can realistically form a majority is with the support of the ten Democratic Unionist (DUP) MPs in Northern Ireland.
The first Labour prime minister, Ramsay MacDonald, took office in 1924 even though Labour had fewer seats than the Conservatives and relying on the tacit support of the Liberals.
The currency market had been expecting a clear victory for Theresa May's Conservative Party, but the results so far, and the exit poll, have cast doubt on its majority, the BBC reported.
Meanwhile, nearly all the constituencies visited by May as part of her bid to win over pro-Brexit Labour voters were held by Jeremy Corbyn's party, with increased majorities.
If Theresa May resigns, Jeremy Corbyn may be invited by the Queen to form a government, either as a minority, or in coalition with another party or parties.
He is committed to heeding the results of Britain's European Union membership referendum a year ago in which 52 percent voted Leave against 48 percent in favour of Remain.
Barry Gardiner, a Labour lawmaker and the party's trade spokesman, said May's early election gamble had threatened Britain's chances of getting a good deal: "We are weaker as a result of her incompetence and indeed her arrogance", he told the BBC. It has also promised to consult parliament more closely throughout the negotiations.
"People have had enough of austerity politics".
"Clearly if she's got a worse result than two years ago and is nearly unable to form a government, then she, I doubt, will survive in the long term as Conservative Party leader".
Whoever forms the next government will oversee one of the most important periods in our country's history so it's not as though the stakes are particularly high...
However, Labour has also committed to creating a 250 billion pound fund for investment in infrastructure which will be spent over a 10-year period, indicating it will be funded by borrowing.
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