Labour was seeking to blame Brexit for the catastrophic electoral defeat predicted by the exit poll that has estimated a huge majority for the Conservatives.
Shadow chancellor John McDonnell was visibly shocked by the 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.
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 in what he described as a “Brexit election”.
“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.”
Mr McDonnell cited “despair” among the electorate at wanting an end to the Brexit saga, adding: “I think this Brexit frustration has broken through.”
On his and Mr Corbyn’s future, he cautioned that the actual results needed to be seen but said: “The appropriate decisions will be made and we’ll always make the decisions in the best interests of our party.”
As was looking likely with Mr Corbyn ramping up his criticism of the media in the run-up to the vote, Mr McDonnell sought to blame a “media campaign against” the leader.
Activists who have canvassed for Labour had been citing Mr Corbyn as being vastly unpopular on the doorstep.
There is little doubt a bitter row will now be played out between different wings of the party as the post-mortem examination is carried out.
Labour’s Dagenham East candidate Margaret Hodge, a vocal critic of Mr Corbyn over his handling of anti-Semitism in the party, said the poll suggested an “utter failure” of “Corbynism”.
Shadow justice secretary Richard Burgon was following the script to blame the “Brexit election” and suggested the party could continue in the same vain saying the next election will be different “given Johnson’s Thatcherite agenda”.
Caroline Flint, a Labour former Europe minister standing in the Leave-backing Don Valley constituency, blamed multiple wings of the party.
“We’re going to hear the Corbynistas blame it on Brexit and the Labour Uber Remainers blaming Corbyn,” she said.
“Both are to blame for what looks like a terrible night for Labour.
“Both have taken for granted Labour’s heartlands.”
A Labour Party spokesman delivered the Brexit-blaming message and sought to defend Mr Corbyn’s legacy.
“We, of course, knew this was going to be a challenging election, with Brexit at the forefront of many people’s minds and our country increasingly polarised,” the spokesman said.
“But Labour has changed the debate in British politics.
“We have put public ownership, a green industrial revolution, an end to austerity centre stage and introduced new ideas, such as plans for free broadband and free personal care.
“The Tories only offered more of the same.”