The Prime Minister signalled the Conservatives will attempt to carry on in Government even in the absence of an overall majority.
Government minister James Wharton was among the Conservative casualties and Home Secretary Amber Rudd’s seat appeared under threat as the prospect of a hung parliament loomed.
The prospects for the Brexit talks proceeding as planned in a matter of days also looked to be receding amid uncertainty over how the next UK government will be formed.
Mrs May’s decision to call a snap poll looks set to rival David Cameron’s EU referendum decision as the biggest miscalculation in recent British political history.
As the polls closed last night, the nationwide exit poll pointed to the Conservatives being the largest party but without a Commons majority.
Senior Conservative figures initially expressed disbelief but by 3am there was acceptance that their worst fears were being realised.
Speaking after her own return as MP for Maidenhead was confirmed, a shaken Mrs May said: “At this time more than anything else this country needs a period of stability and if as the indications have shown and if this is correct that the Conservative Party has won the most seats and won the most votes then it will be incumbent on us to ensure that we have that period of stability and that is exactly what we will do.”
She continued: “Whatever the results are the Conservative Party will ensure that we fulfil our duty in ensuring that stability so that we can all, as one country, go forward together.”
Speculation was already growing in the early hours of the morning that Mrs May may not be able to stay as Conservative leader less than a year after taking over from David Cameron.
Early voting trends suggested younger voters and former Ukip supporters were helping Labour to their far better-than-expected performed.
Labour deputy leader Tom Watson said: “Theresa May thought she was going to get a Margaret Thatcher-style majority. That now seems out of her reach.
“The Prime Minister fought one of the most negative, pessimistic and defensive campaigns in British history and the British people delivered their verdict on that.
“She said she was ‘strong and stable’. The public saw that she was weak and wobbly.
“She said she was a ‘bloody difficult woman’, she boasted about it. The public saw she was just a woman who was finding it all a bit too bloody difficult.”
The exit poll suggested that the Liberal Democrats would make gains over all and former Business Secretary Vince Cable, who lost his seat two years ago, won Twickenham back and former Energy Secretary Ed Davey will also return to the Commons.
But the night saw former deputy prime minister and Nick Clegg lose his seat, while Greg Mulholland lost his Leeds North West seat. Lib Dem leader Tim Farron clung on to his Westmorland and Lonsdale seat, which went to a recount.
The SNP endured losses in Scotland including Angus Robertson, the party’s widely-respected leader in Westminster.
The results of the national exit poll, which has proved highly accurate in recent elections, pointed to the Conservatives remaining as the largest party but short of the 326-seat victory line.
The Conservatives were this morning on track to win 314 seats, a loss of 17 compared to the result just two years ago.