Sooner or later somebody in a position of authority in the Labour Party has to answer the question: why did we lose? We’re not getting answers in the leadership hustings, nor from the National Executive Committee.

As for Jeremy Corbyn’s office, they have been busy securing the leader’s “legacy” – trips to Ghana and Iraq are said to be planned. Before then, I would prefer that those responsible for Labour’s electoral catastrophe take a brief trip to reality.

The contingent reasons Labour lost were obvious on the doorstep, and confirmed by subsequent opinion polls. First, and most importantly, hostility to Corbyn. Secondly, the party’s confused Brexit policy, which caused 1.1 million Remain voters to switch to more unambiguously pro-EU parties, while 800,000 Leavers switched to the Tories. Third, the manifesto, which though meticulously costed, was greeted with incredulity by voters who had bought the logic of austerity.

Behind all this lies a strategically important fact: British politics has become a battle over values and identities – a culture war, in which Labour's traditional offer, based around the economic interests of working-class voters, does not resonate. The task of the party’s leadership was to respond to this new fact: Labour lost because Corbyn, and the officials around him, refused to recognise it.

They were not interested in polls. They did not listen when analysts at Datapraxis told them – right at the start of the election campaign – that they were set to lose tens of seats and needed to go on the defensive. When, on 28 November, they finally accepted MRP polling evidence of a likely Tory landslide, their response was to switch to a crass “retail offer” of policies for small towns, and to continue throwing hundreds of activists at unwinnable seats.

Having stormed around Westminster for the best part of a year, telling Labour MPs “we’re not going to abandon the working class”, figures like Ian Lavery MP and Corbyn’s chief of staff Karie Murphy had no solution to the problem that part of the working class has abandoned us.

The solution they believed would work – to deliver Brexit by enthusiastically voting for it in parliament – was impossible given Labour’s now-overwhelming reliance on BAME voters, the city salariat and young people. The party’s mere decision to enter talks with Theresa May triggered an exodus of voters towards the Lib Dems and Greens, over a million of whom never came back.

To have any kind of meaningful debate about the next Labour leader we need an honest accounting of why we lost. But those closest to Corbyn seem incapable of processing the defeat. This is what’s so telling about Rebecca Long-Bailey’s leaked comments, at a retirement dinner for pro-Brexit former MP Ronnie Campbell. Long-Bailey said she was “crushed” by the exit poll, because while there had been “a few wobbly people on the doorstep” in Salford, “I thought everything was going to be alright”.

I didn’t. Every regional official I spoke to in the 17 constituencies where I campaigned told me we were going to lose. Every candidate I worked with, once away from the canvassing teams, said “it’s a disaster”. And every other candidate for the leadership understood this, days or weeks before the event itself.

Of course it was logical to hope that, with an activist-led campaign, an organic social media strategy, community organising teams in situ and a mass mobilisation to get out the vote on election day, we could limit the damage. And we probably did. But that just underlines the bigger problem: social democracy's traditional weapons of redistribution and universalism don’t work in this new era of warfare.

Despite their differences, the choices of Gordon Brown, Ed Miliband and then Corbyn as leader were underpinned by the same fatal assumption. As long as the leader is able to competently present the economic offer, their accent, style, integrity, honesty and cultural values are secondary.

The 2019 election result showed that this world has passed. The new alliance of conservatism and the far right can win any election it wants to, in England and Wales, until Labour finds a leader who can both represent the values of progressive Britain and then reach across the cultural divide to attract those who don’t share those values.

And that’s why, in the current leadership election, I am focused on the leadership qualities of the contenders first, and their policies second. Labour policy is made by the members – in reality under a veto by left-led trade unions – so there is no chance of a sudden swing back to neoliberal economics or socially reactionary positions on migration, armed conflict or reproductive rights.

Since the majority of the membership wants a left social-democratic government, the sensible question is “who can deliver one?” – and in 2024, not 2029 or beyond. So the left in the party faces a strategic choice. Do we recognise the new situation, and evolve new left policy priorities, new tactics, new modes of organisation? Or is it “Carry On Corbynism” with a different cast?

The experience so far is not encouraging. There are still people at Labour meetings angrily denouncing the Jewish Board of Deputies, and the candidates who've signed their 10-point pledge on anti-Semitism. There are still people more obsessed with “the media” than with asking whether the party itself did something wrong.

In Clive Lewis’s Norwich constituency, at a 500-strong members’ meeting called to discuss the defeat, there was a strong, vocal minority who denounced both Lewis and myself as having “capitulated to the bourgeois Remain lobby” – a phrase many of them read out from pre-prepared speeches. There is, in short, a section of the membership who would be quite happy if Labour were to become a pure, left, bureaucratically centralised party, with every conference reduced to a leadership rally, and the faithful imposed as parliamentary candidates, given positions on the NEC slate or – the ultimate accolade – life peerages. Its meetings would be small and easy for organised minorities to dominate. And it would provide a refuge for committed socialists as they endure long years of Tory rule, in which the welfare state is dismantled and democracy eroded.

If this kind of future appalls you, then the party itself has to become a mass, open, democratic and election-winning alliance. It has to be a cultural and social movement as well as an election machine. And in that project it is leadership skills and personal integrity that are going to matter, alongside commitment to a decarbonised economy and a post-neoliberal economics.

That’s why I am backing Keir Starmer. Starmer is from the left, but can command the trust of Labour’s various centrist wings, as well as the silent majority of members who just want to win an election and stop the agony of food banks, Universal Credit and in-work poverty. Beyond that, experience on the doorstep suggests he is the only candidate with spontaneous name-recognition and popularity among voters who deserted us in December.

When working class people say “I don’t like Corbyn but I would vote for you if Keir Starmer was leader”, it's not out of deference to someone with slick hair and a suit. It's because they sense politics has become a battle of stories, values and ideals and that Starmer stands a chance in that battle, in a way the other candidates do not.

There are risks attached to Starmer. His campaign team is a mixture of the left and centre – with most of the far-left self-excluded – so all the pressure on him is coming from the right. He is cautious on policy: committed to the Green New Deal and to public ownership, but well aware that neither of these properly resonated on the doorstep.

I've talked to numerous Momentum members who are furious at the group’s pre-emptive endorsement of Long-Bailey, but wary of Starmer because they fear he will become another Ed Miliband, swamped by realpolitik and technocratic advisers. In the party hustings, Starmer has to prove them wrong.

But the scale of the challenge means Labour needs a different kind of leader: capable of uniting the party’s factions around the single project of winning in 2025. Above all, we need a leader who understands the new situation, and has a plan to rearm the party morally for the fight ahead, and who can craft our left-wing economic programme into a narrative that reaches across the new political divide. Not one who was flabbergasted by the defeat, who “thought everything was going to be alright”, and whose entire pitch for leadership is that we carry on as before.