Even before the first European election results were made public last Sunday there was talk at the top of the Labour party of a coup against Jeremy Corbyn.

“Tom Watson’s already out, surprise surprise, trying to take on the role of Prince Machiavelli,” said Watson’s former friend turned arch-enemy Len McCluskey, general secretary of the Unite union and close ally of Corbyn. “If he’s trying to turn Labour members against Corbyn and in his favour, then he’s going to lose disastrously.” McCluskey was reacting to an article Watson had written in the Observer that day saying that Labour would suffer a repeat of what he predicted would be terrible European election results at the next general election unless it ended its “mealy-mouthed” approach to Brexit.

McCluskey, who seems to hate the idea of a second referendum on Brexit almost as much as he dislikes Watson, wanted to paint the deputy leader as a rogue plotter, interested more in his own pursuit of the leadership than the good of the Labour movement and the country.

Within a few hours, however, as the disastrous results showed Labour had lost 11% of its vote share and half its seats in the European parliament, leaving it with none at all in Scotland, it was not Watson who seemed out on a limb but McCluskey and the small Corbyn inner circle of which he is part. It is this group, which includes the party chairman Ian Lavery, that has steadfastly resisted backing a second public vote on Brexit, believing the result of the referendum should be honoured and that many Brexit-backing Labour supporters would never forgive the party if it allowed Britain to stay in the EU.

Tom Watson was accused of trying to turn the party against its leader. Photograph: Dominic Lipinski/PA

One after another, senior Labour figures went public, echoing Watson and demanding that the party stop sitting on the fence on Brexit. The evidence was clear, they said, that Labour’s Remain backers had deserted the party in huge numbers, moving to the Lib Dems and Greens, outnumbering the Leavers who had gone to Nigel Farage’s Brexit party.

First out of the blocks was Emily Thornberry, shadow foreign secretary, who demanded that Labour act immediately to change policy because a new Tory leader could soon back a no-deal Brexit and ruin the country. “No deal would be a disaster,” she said. “There should be a referendum and we should be campaigning to Remain.”

But it was not only moderates like Thornberry. Corbyn supporters on the left were joining in, too, including his closest political ally John McDonnell. Before the final results were in, the shadow chancellor said the previous approach of pushing for a general election was not going to work. “Of course we want a general election,” McDonnell said. “But realistically after last night there aren’t many Tory MPs that are going to vote for a general election. It would be like turkeys voting for Christmas.

“So our best way of doing that, I think, is going back to the people in a referendum, and I think that’s what our members want.”

Len McCluskey has attacked those wanting a second Brexit referendum. Photograph: Chris J Ratcliffe/Getty Images

Then the Corbyn-supporting journalist Paul Mason wrote an excoriating article in the Guardian under the headline “Corbynism is now in crisis: the only way forward is to oppose Brexit.” Mason stuck the knife into Corbyn and his close-knit team of advisers, naming Seumas Milne, his director of strategy, and Karie Murphy, his chief of staff, who is a close friend of McCluskey.

“Since December, Corbyn and his advisers have got the Brexit strategy badly wrong … The campaign execution was dire from the top down,” said Mason, adding that “the officials who designed this fiasco and ignored all evidence that it would lead to disaster must be removed from positions of influence”.

What McCluskey had tried to pass off as a doomed coup attempt led by the lonely figure of Watson seemed to be becoming the consensus view across much of the party.

The past week has arguably been the worst for Corbyn since he saw off a genuine coup attempt by his own MPs in 2016. And it has all gone wrong at a time when the Tories’ epic civil war over Europe, leading to the fall of Theresa May, should have seen Labour consolidating its bid for power. Losses in the European election not only reopened arguments over Labour’s Brexit policy but unleashed vicious personal spats that climaxed with the decision on 28 May to expel Alastair Campbell, Tony Blair’s former spin doctor, from the party for having voted – like many, many other Labour members – for the Liberal Democrats.

Emily Thornberry says Labour must campaign against a no-deal Brexit. Photograph: Oli Scarff/AFP/Getty Images

The party will not say which official took the decision but fingers have been pointed at Murphy and Milne. Senior figures from all the wings of the party were appalled at what they saw as a wildly provocative and unnecessarily divisive move. An #expelmetoo backlash took off on social media.

Betty Boothroyd, the former Commons Speaker and ex-Labour MP, said: “The Labour party seems incapable of making positive leadership decisions of late. Fence-sitting seems to be in vogue. But the decision to expel Alastair Campbell from the party is the daftest, most insensitive decision of all.

“For the first time in my long life I didn’t vote Labour at the European elections, and there are no prizes for guessing where my vote went.”

Several senior members of the shadow cabinet have made known their dismay to the leader’s office and will demand that the decision be overturned when MPs return to the Commons this week. Watson has already described the move as “spiteful” and said he wants it reviewed.

Seumas Milne has been accused of getting the Brexit strategy wrong. Photograph: Facundo Arrizabalaga/EPA

Some Labour MPs believe the Campbell decision was taken deliberately in the hope of rallying Corbynites and distracting attention from an announcement (that broke on the same day) by the Equality and Human Rights Commission that it was launching an official inquiry into Labour’s handling of antisemitism complaints under section 20 of the Equality Act 2006.

The commission said it would seek to determine whether the party and its employees had committed unlawful acts of discrimination or failed to respond to complaints of unlawful acts in an efficient and effective manner.

As it turned out, the equality commission’s move and the Campbell row combined into one toxic mix. Wes Streeting, the Labour MP for Ilford North, was one of many who drew attention to the “stark contrast between the ruthless speed of the Alastair Campbell expulsion and the constant foot-dragging over antisemitism cases”, both of which, he said, revealed much about decision-making in the leader’s office.

To cap it all, on 31 May the party suspended Pete Willsman, a member of its national executive committee, after he was recorded saying that an Israeli agent had infiltrated the party and that the Jewish state had stirred up much of the row over antisemitism. It was the second time in 10 months that Willsman had been suspended over alleged antisemitism – but unlike Campbell he was not expelled.

John McDonnell says party members want a referendum. Photograph: Andy Rain/EPA

Over the past month Labour has gone backwards in two sets of elections at a time when the Conservatives have all but lost the ability to run the country. On Saturday the latest Opinium/Observer poll put Labour down seven points from a fortnight ago, on 22%. Incredibly, it is behind Nigel Farage’s Brexit party, which is now the most popular force in the country on 26%.

The Tories are on 17% (down five points) and the Liberal Democrats on 16% (up five points). There is much concern within the shadow cabinet over whether the lost votes will return. “The worry is that once people break the habit of voting Labour, that is that, they don’t come back,” said one shadow cabinet member.

Increasingly, senior figures are demanding an end to fence-sitting on Brexit, and there are signs that the leadership is listening. Immediately after the European elections, Corbyn appeared to be warming to the idea of a second referendum but then on 30 May suggested he still backed a soft Brexit and said another public vote was still “some way off”.

Today, writing in the Observer, the former Labour home secretary David Blunkett says there is no question of a coup against Corbyn himself, but says a way must be found to get him to change the personnel around him.

“In my view, there are two forces within the Labour movement – the unions and Momentum – who must now act to get rid of those key advisers who are a block on policy changes and who are responsible for the incompetence we are seeing,” Blunkett says.

David Blunkett called for those around Jeremy Corbyn to be removed. Photograph: Oli Scarff/Getty Images

David Martin, Labour’s longest-serving MEP, who lost his seat representing Scotland, went further, saying that if Labour did not change into an unequivocally Remain party it would be “wiped out in Scotland and in other parts of the country”. He added: “If Jeremy Corbyn is not prepared to make this change, he should his consider his position. The buck stops with the leader.”

This week the pressure will intensify as Labour MPs return to Westminster after the Whitsun break. On 4 June pro-Remain shadow cabinet ministers will demand both that the party moves on Brexit and that it reinstates Campbell. There will be resistance, no doubt, from some close to Corbyn, including Lavery.

Then, on 6 June, the party will await the result of a byelection in Peterborough caused by the conviction of the former Labour MP Fiona Onasanya for lying about a speeding ticket. Labour hopes to win the seat back. A hat-trick of election failures, however, would see Corbyn and his inner circle looking more isolated than ever.