Those who believed that a leftwing prospectus would inevitably condemn Labour to electoral oblivion now have a choice. In last month’s election, it gained seats for the first time since 1997 and achieved its greatest surge in vote share since 1945. The party now has a real – though not inevitable – chance of government. Critics can therefore accept that their narrative is fatally wounded. Or they can abandon claims that they opposed Jeremy Corbyn on electability grounds and admit it was the desirability of his ideas that underpinned their objections. This is the honest and principled position that, for instance, Tony Blair’s former speechwriter Philip Collins has taken.

There are those Labour MPs who saw centrism as an undesirable but necessary formula to win a general election and transform their constituents’ lives. But there are others who remain ideologically and emotionally wedded to centrism and balk at the idea of a leftwing ascendancy in the Labour party. Their beliefs were partly forged as a reaction against leftwing mantras. One of their founding texts is Hammer of the Left by John Golding, a leading figure on Labour’s right in the 1980s, detailing his role in the fightback against Bennism. In 1983, Labour’s right acquiesced to the party standing on a radical manifesto in the hope that the ideas would be buried in electoral Armageddon. They believed the same would happen this time. It didn’t, and now it’s their turn to reassess.

Two big caveats. One, I was someone who originally backed Corbyn for leader but who ended up believing Labour’s poor polling could not be turned around. I was completely wrong. Two, Labour today is overwhelmingly united, because there were many MPs who thought Corbyn’s policy offer desirable but unelectable. But the exceptions need to be challenged before their arguments gain traction.

Take Phil Wilson, Tony Blair’s successor as Labour MP for Sedgefield. Nine months ago, he tweeted an article titled “Jeremy Corbyn will lead Labour into electoral oblivion – and that’s a disaster for Britain”. Now, with that prediction confounded, he offers a deeply misleading postmortem. While the Labour right once castigated the left for its inability to win over middle-class voters, Wilson now accuses Corbyn’s Labour of being too middle-class. “Labour’s campaign struck a chord with the young, especially students,” he claims. Polling suggests Labour in fact attracted its greatest support among working-class voters under 35, and that its majority among young middle-class voters was significantly smaller.

“The middle classes rallied to the causes,” writes Wilson. “Working people, on the other hand, favoured the Tories.” But the post-election polling flatly contradicts this assertion. According to YouGov, Labour had a lead among both part-time and full-time workers. And Ipsos-Mori has estimated that among what pollsters call “DE” voters – the semiskilled and unskilled working class, and those out of work – Labour had a nine-point lead. Corbyn increased Labour’s vote share among working-class voters compared to 2015.

Reading Wilson’s analysis – similar to that which has circulated throughout the media since the election – you would be left with the impression that Labour had lost working-class support, rather than gaining it. What is true is that Ukip’s collapse infused the Tories’ own electoral coalition with older working-class voters. In Ashfield in Nottinghamshire, for instance, Labour’s Gloria De Piero increased her vote, but the Tories nearly doubled theirs. That largely explains the overall working-class swing to the Tories. Labour does need to win these voters over. But let’s stop implying that the 40% who voted for Labour – around two percentage points fewer than the Tories – is awash with trendy middle-class bohemian types.

Labour would not win by “travelling only the middle-class streets of Kensington” or university campuses, is Wilson’s response to an argument that no one is making. Millions of working-class and middle-class Britons voted to tax the top 5% more to invest in the economy and public services, to introduce a living wage, to bring utilities into public ownership, confront the housing crisis, and rid students of the burden of debt. Is that not an achievement worth building on?

I have another fear, too. Some on Labour’s right understand that their route back to the party leadership is all but nonexistent. There may well, then, be the temptation to drive a wedge between the leadership and the party’s younger voters over the EU. Labour’s internal differences are rather more nuanced than they are portrayed: almost all Labour MPs want concessions from the EU, which will make full membership of the single market difficult, if not impossible. It would be a mistake to wrongly portray the leadership as pursuing the same form of Brexit as the Tories in the hope that this will nurture disillusionment among younger votes, not least as the reality of the referendum result begins to hit. Some on the Labour right may believe they can capitalise on this backlash. But the election result was about far more than Brexit or indeed tuition fees, as some commentators suggest. It was Labour’s overall vision that tapped into a growing desire for Britain to be governed by a different social order than one that breeds insecurity and stagnation.

And now, there can be no going back, for any retreat would mean going back to the compromise of 2015, which inspired few and alienated many. Labour does urgently need to address its deficit among older voters, and its doggedly pro-pensioner stance will help win inroads. It needs to expand the electorate further, mobilising even more younger and previous non-voters. It needs to expand its foothold in Scotland. There are no shortage of marginal Tory seats that are in reach because the Tories are in crisis, unable to make the ideological case for their politically bankrupt ideas any more. Labour’s right risks retreating into the same cul-de-sac it often accused the left of residing in: stuck in the past, inflexible, dogma over evidence. But a retreat to Labour’s old formula, at a time when Britain is convulsed by multiple crises, would be a tragedy, and a fatal mistake.