One morning late in the autumn of 2015, I was told by a Labour MP that Jeremy Corbyn was struggling to manage his workload and was likely to stand down by the summer. But the deadline passed and by the summer of 2018 I was being told that the Labour leader was suffering from the early signs of dementia and would soon announce his departure. Then, as autumn turned to winter, the illness had changed: now Corbyn was meant to have suffered a minor stroke that would force him out of office.

At the start of his leadership, it was often said that Corbyn was kept in office thanks to the manipulation of his then chief of staff, Simon Fletcher, who emerged from the Trotskyite groupuscule Socialist Action. Now, we are told, he is held in place by his spin doctor and strategist Seumas Milne, a former Guardian journalist who began his career on the Stalinist magazine Straight Left. Sometimes, the rumours are different and it is John McDonnell, the shadow chancellor, who is propping up his old friend’s failing body. At other times, McDonnell is doing his utmost to ease Corbyn out of the door. That the rumours about Corbyn’s health have been circulating for so long, and that many of the essential figures around Corbyn have moved on, hasn’t stopped the whispering. That the leader’s office has been unable to keep the news that Corbyn is receiving treatment for a minor eye problem at Moorfields Eye Hospital out of the papers – and that the contents of emails are regularly leaked to the press – should disabuse most people of the notion that his team were successfully covering up a stroke. But the stories persist.

In the Times on 29 June it was reported that senior civil servants had speculated that Corbyn was “too frail” ever to become prime minister. Many Labour insiders have blamed Mark Sedwill, cabinet secretary, head of the civil service and, crucially, a former Home Office mandarin, for the comments. They believe that Sedwill is particularly opposed to the idea that a lifelong civil libertarian who would doubtless seek to upend decades of foreign and security policy consensus could soon be in Downing Street.

The Labour leader has called for a full inquiry into the Times story, which is perfectly calibrated to push Team Corbyn’s buttons. It speaks to their (not unreasonable) sense that much of the press is not only hostile to Corbyn, it refuses to take him seriously, seeing his leadership as an eccentric pause before normal service resumes. And it reinforces the secret fear that even should Labour take office, it will be undermined from within.

That worry is sometimes voiced in all seriousness and sometimes is expressed humorously. Milne, who dislikes cold weather, recently joked that he would support a bloodless coup to remove Corbyn from office, provided that he was bought off with a sinecure in Barbados or some other tropical climate.

Why do the stories persist?

The dull truth is that whispers about Corbyn’s health are a form of comforting escapism for his internal critics. Corbynsceptics know that they have a leader they do not like and cannot change. They do not want to join an explicitly centrist party such as the Liberal Democrats and are even more opposed to what they see as the doomed ego trip of the breakaway Change UK, now led by Anna Soubry, a former Conservative. Corbynsceptic MPs and staffers gather together, commiserate over their plight, look at the options outside of Labour, find them wanting, and sooner or later, in a mood of gallows humour, someone or other will speculate that perhaps Corbyn might stand down, or die in office. A form of Chinese whispers means that one MP’s comfort blanket becomes another Labour staffer’s gospel truth.

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It’s no surprise that the rumours tend to flare up after periods in which the Parliamentary Labour Party (PLP) is particularly frustrated with its leader. The truth about Corbyn, who is 70, is that if he won an election he would be the oldest politician in more than a century to become prime minister for the first time. His eyesight is worse than it was when he became leader in 2015 – he occasionally texts Diane Abbott, a close ally, in shadow cabinet meetings, and the size of the text on his screen is now large enough that nearby officials and MPs “don’t even have to try” to read the messages.

Then there are Rebecca Long-Bailey’s travels around the country. The shadow business secretary is spoken of as a potential successor to Corbyn, and so you can see why MPs are adding two and two together and making five.

The reality is that Corbyn is not planning to step down – he runs and exercises and friends say he has not had a minor stroke – though he is, as one close observer puts it, “fed up and fucked off” at the state of politics and the Labour Party. He does not understand and is personally upset by accusations that he is either culpable for the rise of, or an active producer of, anti-Semitism in the party. He is unhappy that Labour’s equivocations on Brexit have put him on the wrong side of many of his long-term allies in his Islington constituency and of his two closest allies in the shadow cabinet, McDonnell and Abbott.

But the stories will persist because Corbyn is not the only Labour MP who is “fed up and fucked off”. The immediate concern for almost every Labour MP is that the party has brought forward the process of reselecting sitting MPs, the so-called trigger ballot process. In 2017, the snap general election meant that every incumbent Labour MP was waved through without having to seek the re-endorsement of members. That missed opportunity rankles with some of Corbyn’s closest allies for ideological and strategic reasons.

Ideologically, Corbyn is committed to the principle that Labour MPs should undergo a genuine reselection process from their activists, while strategically, the PLP is now the last bastion of the old pre-Corbynite party. Reshaping the PLP will both entrench the leftist transformation and, some more wonkish Corbynites point out, provide vital personnel for the lower reaches of a Corbyn-led government.

The season of trigger ballots is stressful, although Labour MPs have an easier path to reselection than those of any other party. Liberal Democrat, SNP and Plaid Cymru MPs face a straight “one member, one vote” ballot of their local parties to be readopted as candidates, while Conservative MPs have to undergo a vote by their local executives. Labour activists who want to remove their MPs must clear a complex series of procedural hurdles to trigger a selection process – though the system has been simplified by the leadership in order to facilitate a greater number of full-blown selection contests.

No one really knows what the impact of the rule change will be, but many Labour MPs are worried. More than 30 took part in a deselection seminar organised by Tom Watson’s Future Britain Group, a talking shop for Corbynsceptic Labour MPs, and demand for the event was sufficiently high that another will take place.

The meeting, which one MP present described as “half group therapy, half organisational strategy”, was chaired by Gloria De Piero, who leads the Future Britain’s incumbency and campaigning group. De Piero owes the role to her success in winning Ashfield twice by close-fought margins, against the Liberal Democrats in 2010 and the Conservatives in 2017. Several who attended said it recalled meetings of MPs in marginal seats. “It’s mostly hypothetical questions: what if this happens? What if that happens? It’s really just people trying to work out how to organise to get re-elected, except in the party not the country.”

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No one at present talks seriously of reviving Labour’s fortunes in Scotland and, with the SNP resurgent, many concede that most of the party’s seven MPs there are unlikely to return to Westminster. Most MPs in the Welsh party now loudly support a second referendum and the Labour leader in Wales, Mark Drakeford, has embraced the People’s Vote campaign.

If Labour MPs in Scotland and Wales are worried about nationalists, in England it is Brexit that is causing most unease. Labour MPs in England are split into three camps: those who fear the Brexit Party, those who worry about the Liberal Democrats and Greens, and those who are nervous about all three. According to Labour’s own analysis, the party loses three votes to Remain parties for every one it loses to the Brexit Party – but the distribution of those votes under the first-past-the-post system means that both are lethal.

And yet, there is some hope. At the top of the Labour Party, they seriously believe that someone is running to save them: Boris Johnson. One Corbyn ally says that a Johnson-led Conservative government would “put things into perspective” for disaffected Remainers.

Another says that Labour has done best “when politics are polarised”: a Conservative leader whom Liberal Democrat voters do not loathe would make it easier for Remainers to abandon Labour in marginal seats. Johnson will make it harder for Remain voters to risk voting against Labour, for fear of something worse. The view is not confined to Corbynite loyalists: Jess Phillips, the outspoken backbencher, has described a Johnson leadership as “a gift” to Jeremy Corbyn.

Are they right? If the polls are to be believed, a Johnson premiership would simplify the task before Labour. But just as Theresa May gambled in 2017 that dislike of Corbyn would rescue her own flagging election campaign, Labour believes a repellent Conservative Party led by Johnson will save it. The bet may play out no better for Corbyn than it did for May.