With Britain apparently heading for a hung parliament, Mrs May pledged to offer ‘stability’ if the Tories end up as the largest party with the most votes, as expected.
But Conservative former minister Anna Soubry said she should ‘consider her position’ and take personal responsibility for a ‘dreadful’ campaign and a ‘deeply flawed’ manifesto after choosing to go to the country three years early in the hope of extending her majority.
Labour leader Jeremy Corbyn called on the Prime Minister to resign, saying she should ‘go and make way for a government that is truly representative of this country’.
And former chancellor George Osborne, sacked from the Cabinet by Mrs May and now editor of the Evening Standard, told ITV: ‘Clearly if she’s got a worse result than two years ago and is almost unable to form a government then she I doubt will survive in the long term as Conservative party leader.’
With 606 out of 650 constituencies declared, a Press Association forecast predicted that Tories would end up with 319 seats - 11 fewer than when the election was called and seven short of an absolute majority. Labour was heading for 261 seats, the Liberal Democrats for 14, the Scottish National Party 34, Plaid Cymru three and Greens one, according to the PA analysis.
A BBC projection put the Tories on 43% overall - about six points up on David Cameron’s result in 2015 - and Labour on 40%, outpolling Ed Miliband and Gordon Brown’s results and even racking up more votes than Tony Blair did when he won power in 2005.
The pound plummeted as the shock figures set the scene for political turmoil at Westminster, disruption to upcoming Brexit negotiations and the possibility of a second election later in the year.
The night was marked by a collapse in Ukip support and a rash of high-profile losses for the SNP, as British politics returned to a two-party system on the greatest scale since the 1970s.
The Tories lost four frontbenchers, with Treasury ministers Jane Ellison and Simon Kirby and housing minister Gavin Barwell going down to defeat, along with Cabinet Office minister Ben Gummer, the author of the widely criticised Tory manifesto.
Ukip leader Paul Nuttall faced humiliation in Boston & Skegness, where he came in a distant third in one of his party’s top target seats.
As Ukip voters switched to Labour and the Tories across the country, Mr Nuttall said Mrs May had put the Brexit process in ‘jeopardy’ just 10 days before talks were due to begin in Brussels.
High-profile casualties of a night of shock defeats included Liberal Democrat former leader and ex-deputy prime minister Nick Clegg in Sheffield Hallam and SNP former first minister Alex Salmond in Banff & Buchan.
Home Secretary Amber Rudd and Education Secretary Justine Greening hung onto their seats by the skin of their teeth with much reduced majorities.