Labour appears to be on course for a catastrophic electoral defeat after the exit poll estimated a huge majority for the Conservatives.
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.
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.
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 though the polls were narrowing.
"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."
