Jeremy Corbyn blamed the "polarising" Brexit debate for Labour's dismal electoral showing, as he confirmed he would not lead the party into another general election campaign.
Labour Party figures have already begun pointing the blame at either Mr Corbyn or Brexit as the defining reasons for their catastrophic electoral defeat, as predicted by the broadcasters' exit poll.
Forecasts predict Labour will suffer their worst electoral defeat since 1935.
In a speech at his Islington North constituency, Mr Corbyn said his party's policies were popular with the country but that "normal political debate" had been eroded by Brexit.
Mr Corbyn said: "This is obviously a very disappointing night for the Labour Party with the result that we've got.
"All of those policies were extremely popular and remain policies that have huge popular support across this country.
"However, Brexit has so polarised and divided debate in this country, it has overridden so much of the normal political debate and contributed to the result for the Labour Party across the country."
The Labour leader refused to say whether he would immediately resign, hinting that he would instead stay in charge while the next leader is chosen.
He said: "I want to make it clear that I will not lead the party in any future general election campaign.
"I will discuss with our party to ensure there is a process of reflection on this result and on the policies that the party will take going forward.
"I will lead the party during that period to ensure that discussion takes place as we move on into the future."
Moderate figures within the party, such as former shadow cabinet members Ed Balls and Alan Johnson, pointed the blame at Mr Corbyn's "disastrous" leadership.
Meanwhile current shadow cabinet members Dawn Butler and John McDonnell said Brexit had proven to be the party's downfall.
Mr Johnson, who served in a number of cabinet positions under Blair and Brown governments, was critical of Mr Corbyn's leadership and the left-wing Momentum group, set up by Jon Lansman, which has backed the Labour leader throughout his tenure.
Speaking on ITV News following the exit poll, Mr Johnson said: "Corbyn has been a disaster on the doorstep. Everyone knew that he couldn't lead the working class out of a paper bag.
"Now Jon's developed this Momentum group, this party within the party aiming to keep the purity. The culture of betrayal goes on.
"You'll hear it now more and more over the next coming days as this little cult get their act together.
"I want them out of the party. I want Momentum gone. Go back to your student politics."
Ed Balls said: "We've just seen the lowest number of Labour MPs in our history, the biggest fall in our voting share in our history.
"Jeremy Corbyn has now lost two elections... so don't we just have to reach a conclusion from that?"
However Mr Lansman said the Labour Party's policies under Mr Corbyn were popular with voters.
He said: "On austerity, he has completely changed the narrative, the narrative which Ed Balls tried to change with his Bloomberg speech but failed to deliver on.
"Jeremy Corbyn even before he became leader destroyed the universal assumption that there was no choice but to deliver austerity, such that the Tories are no longer pursuing that narrative."
Meanwhile Shadow Equalities Minister Dawn Butler told ITV News: "Ultimately this defeat will be down to one thing, and that'll be Brexit."
Shadow chancellor John McDonnell was visibly shocked by the predicted figures suggesting Labour was on course for its second General Election defeat under Jeremy Corbyn.
Mr McDonnell sought to blame a public discourse in which “Brexit has dominated”, defended the left-wing policies adopted by him and Mr Corbyn, and said “appropriate decisions” will be made about the future of the leadership.
Labour's Lucy Powell urged party members to avoid "knee-jerk" reaction about who was to blame for the result.
She said it was important to take a "long, hard look" over the past few years as to the reason behind their polling performance.
The Manchester Central Labour candidate said: "It's a number of things. Of course Brexit is one of them. I think its obviously our offer to the public and all of that in the round looks like its been rejected this evening.
"If its on this sort of scale that the exit poll and some of the early results suggest, I think the worst thing we could do is to just have a knee-jerk reaction and say 'I know what it was' based on our own preconseptions.
"I actually think that such a scale result like that suggests that we need to take a long, hard look not just at this election, but over a number of years, and start to chart a course back to us to be electable and appealing to the public.
She added: "I don't think blaming it on just Brexit or just Corbyn or on something else, I don't think that will serve us well in the long-term."
The BBC/Sky/ITV poll suggested Labour had slumped to 191 seats while the Tories had surged to 368 and winning a majority of 86, paving the way for the UK to leave the EU next month.
If the actual result resembles the prediction, Labour will lose 52 seats, putting it on course for its worst result in terms of seats since 1935.
Mr Corbyn will now be under overwhelming pressure to resign. Ahead of the election, Labour sources had been predicting he would only go if Boris Johnson won a majority.
But they indicated Mr Corbyn would not resign immediately if he had no chance of becoming PM and would likely stay on into the new year while a leadership election is battled.
Shortly after the poll was released, Mr McDonnell told the BBC he was shocked by the prediction, having thought the polls were narrowing.
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“If it is anywhere near this it will be extremely disappointing for the party overall and for our movement,” he said.
“I think Brexit has dominated, it has dominated everything by the looks of it.
“We thought other issues could cut through and there would be a wider debate, from this evidence there clearly wasn’t.”
Asked about his and Mr Corbyn’s future, he said: “Let’s see the results themselves, as I say, the appropriate decisions will be made and we’ll always make the decisions in the best interests of our party.”