After the thrill of hearing his name turned into an anthem at Glastonbury – “Oh, Jer-e-my Cor-byn” the crowd serenaded his act on the Pyramid Stage – the Labour leader had a chat with Michael Eavis, the founder of the festival. Mr Eavis asked the other man when he would become prime minister and says he got the reply “in six months”.

That response would once have had even Mr Corbyn’s most devoted admirers wondering whether he had overindulged on some hallucinogenic substances. Before 10pm on 8 June, his inner circle thought the post-election challenge would be to prop him up for long enough to try to secure the succession for a younger torch bearer from the left of the party. That assumption, like so many others, has been smashed by what the voters did. “He has changed since the election,” says one Labour MP who specialises in Corbyn-watching. “Jeremy has morphed into someone who wants to be prime minister.” Tories who once laughed at that notion now take it seriously. The spectre of prime minister Corbyn haunts the corridors of Conservative minds. An important reason why they are flinching from dispatching their failed leader is the fear of precipitating another election which could propel Mr Corbyn into Number 10.

There’s another paradox. Though they are back in office, the Conservatives are conducting an extremely visible post-mortem into what went wrong for them. Though it remains in opposition, Labour is not going through an agony of public introspection about its performance. All Labour MPs are expected to bend the knee to the glorious leader for getting the party over the 40% threshold. Any Labour figure who has the temerity to caveat the adulation by mentioning that the party still lost is at risk of being arraigned for apostasy.

The 'one more push' school holds that 8 June proves Labour can win

So it is a little bit brave of Tom Watson to raise this awkward topic in the interview that we publish today, especially when the Corbynites are already after the deputy leader. His shadow cabinet colleague, Emily Thornberry, has said that the party needs just “one last push” to acquire power. By arguing that it might not be quite so simple, Mr Watson lifts the lid on one of the post-election arguments in the party’s ranks.

The “one more push” school holds that 8 June proves Labour can win with a left-wing programme and that the country has completely reappraised its once dim view of Mr Corbyn’s potential to be a successful prime minister. The same anti-austerity message, only more of it and even louder, will get them over the line next time. This view is encouraged by post-election polls which report continuing movement to Labour and the leader’s personal ratings, which once plumbed record depths for an opposition leader, shifting into positive territory. The Opinium poll that we publish today has Labour ahead by six points.

This gives a patina of credibility to the view of John McDonnell, the shadow chancellor, that his friend would already be in Number 10 had the election campaign lasted another fortnight.

The “more to do” school notes that Labour came in 55 seats behind the Tories and requires a swing roughly double that achieved on 8 June to become a majority government. It would be a bold Labour MP who said this aloud in the current atmosphere, but quite a lot of them furtively think that the election result was a bit of a freak, the product of a confluence of factors that were perhaps uniquely favourable. The Tories fought an abysmal campaign on a manifesto that had nothing positive to offer. Up against Mr Corbyn, a man who thrives on electioneering, the Conservatives fielded the malfunctioning Maybot, a leader who proved useless at retail politics. “We won’t be that lucky again,” says one senior Labour figure. Some also believe that Labour benefited because no one expected it to be in a position to implement its manifesto and they’d best prepare for the party’s prospectus facing much fiercer scrutiny next time around.

Both sides of this argument can marshal some evidence to support their view. The Corbynites were correct to say that they could get younger voters to turn out in bigger numbers. It is patronising to suggest that “the youth” were swept up by a shallow “Corbynmania”. A study by Michael Bruter, professor of political science at the LSE, suggests that the biggest motivators for young Labour voters were the desire for change and opposition to Brexit plus the allure of the pledge to scrap tuition fees. It wasn’t just the young. Even more important to Labour’s performance was support from 25- to 44-year-olds, especially university graduates.

If these generations maintain an allegiance to Labour as they age and are supplemented by support from fresh voters, then this would be excellent for the party’s future prospects.

Labour did well among the affluent ABs. Fans say this proves that Corbynism can be just as appealing to the middle classes as Blairism

Where Labour did strikingly badly was among voters old enough to have lived in the 1970s. The Tories wilfully aggravated the silvery vote, not least with Mrs May’s social care policy which was doomed as soon as it was dubbed a “dementia tax”. Labour’s cornucopia of spending promises included pledges to older folk, even the richest of them, that they could keep all the welfare perks of being a pensioner such as the winter fuel payment and triple-guaranteed rises in the state pension. Yet Labour was still massively behind the Tories among the over-55s and even more so among the over-65s. In a recent meeting with his MPs, Mr Corbyn acknowledged that he had “a problem” with this demographic.

Another fascinating feature of the election was the realignment of traditional party allegiances based on social class. Labour did well among the more affluent ABs. Fans say this proves that Corbynism can be just as appealing to the middle-classes as Blairism once was. Labour also won at the opposite end of the social spectrum. The party’s support is increasingly concentrated among the highest and the very lowest earners; Labour MPs sit for seats as wildly different as Canterbury and Knowsley. Where Labour really struggled was with the C2s, people often characterised as the “just about managing”. The Tories added a lot of support among this crucial segment of the electorate.

This challenges the notion that the election can be entirely explained as a revolt against austerity. That was a component, but if it were simply about that Labour should have done much better with this group. An analysis by the think tank Policy Network to be published this week will argue that Labour can’t win a majority unless it appeals to many more of the lower and middle income folk who are currently the least convinced that Labour’s programme adds up. Tom Watson says these voters need much more reassurance on “policing and security”, which is his coded way of saying that they don’t trust Mr Corbyn with their safety.

I don’t detect any great inclination in the Labour leader to heed all this unsolicited advice to adjust his strategy. He has spurned offers from more centrist figures to broaden Labour’s team by coming back into the shadow cabinet. He has just sacked three frontbenchers who broke the party whip when they voted in favour of Britain remaining within the single market. His allies want to exploit the Corbyn surge to tighten their grip on the party. They ask – and, of course, they have a point – why they should take any tips on how to win from people who were only recently predicting a Labour meltdown?

Labour played what turned out be a clever double game at the election

It might, though, be ill-advised to ignore the evidence that Labour has a big problem with people on lower and middle incomes, especially working-class voters in its traditional heartlands. Natascha Engel, a well-regarded MP, was unseated by the Tories in North-East Derbyshire, the first time that seat hasn’t been Labour since 1935. She says: “What we need to do is reconnect with our white working class voters.”

Deborah Mattinson, the strategy director of Britain Thinks, was involved in her first Labour campaign in 1987. She can’t be dismissed as a Tory stooge. After conducting extensive focus groups with swing voters in six marginal seats, she reports: “There were as many who voted Labour in spite of Corbyn as did because of Corbyn.”

That chimes with the views of the many Labour MPs who are still Corbyn-sceptics. They are keeping their heads down at the moment for fear of being monstered by Momentum activists and targeted for deselection, but their secret view is that the election result was not proof of a resounding endorsement of Corbynism. “Given that no one thought Labour could possibly win, it was a massive protest vote,” says one of their number. While that sounds over-simplistic, it is certainly true that Labour played what turned out to be a clever double game at the election. While the Labour leader enthused the converted at his energetic rallies, many of his candidates were on the doorstep telling doubtful voters that it was safe to vote Labour because there was not a cat in hell’s chance of the party getting into government.

Being the underdog worked to the benefit of Labour on 8 June and perfectly suited its leader’s style of insurgency politics. I don’t presume to make a prediction, but it is fair to say that the dynamics of the next election will be very different.