Nominations are closed, so ballot papers go out at the end of the week to some 580,000 Labour members and supporters to choose a new leader. Three candidates enter the final furlong, still travelling the country in a last parade of hustings. The 4 April finishing post still seems far away as they strive for something new to say, each tiptoeing around the perimeters of a deeply split electorate. Their campaigns now have membership lists: everyone is bombarded.

Inside Keir Starmer’s phonebank his volunteers were speed-dialling: unlike the recipients of the hell of cold calling, this pool of fully engaged citizens, the rare numbers who belong to a political party, are keen to talk. I spoke with members from Midlothian to Walsall, Bolton to Bedfordshire, Norfolk to Deal, all with tales of the politics of their towns, their general election catastrophes – and the great divide between them.

Voices from a riven party included Jim from Birmingham. His local party nominated Starmer, but on a tiny turnout. “Not me, absolutely not Keir. He’s a Trojan horse, a suited-and-booted knight of the realm, a triangulator on the side of MPs who tried to vote out Jeremy Corbyn.” Which of his policies does he oppose? “He won’t introduce open selection of MPs. I’m disgusted by most Labour MPs’ behaviour in the last years.” Trigger ballots to reselect Labour MPs poisoned local parties, wastefully burning energy and emotion before being suspended in the run-up to the general election, so is that really what matters most after four election defeats? Yes, it seems so for members such as him: “Keir’s in with the MPs who say they’ll quit if Rebecca Long-Bailey wins.”

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But Andy from Leicester said the opposite: “I’d leave immediately if Long-Bailey wins. So would most people I know. I’ve barely clung on for the last five years. Mind you, I’ve been disappointed in Keir’s list of 10 pledges – [he’s] still going to nationalise everything, too left.” He sighed. “Yes, I guess he has to say that to get elected, it has to be.”

Here’s Dora from Oxford backing Long-Bailey: “If Keir wins, it’s going back to the Blairites, PFI hospitals, the Iraq war. We’d be going back on everything we’ve gained in the last five years. We’ve got the party right for the first time.” Chris from Bedfordshire agrees: “Keir’s too centrist. We’ve fought this long for an intellectually socialist party. But – well, I don’t know – maybe to win we have to go with Keir all the same.”

Most were strongly for Starmer, though a few gloomily sought to dodge the critical choice by opting for Lisa Nandy, who has indeed had a good campaign. This was no straw poll, but a random flavour of what all members know: this visceral tug-of-war will set Labour’s destiny, even the survival of the party as a serious contender for power. On one side are those who believe the capture of Labour for a purer socialism is all that matters in the long run, looking to far horizons several elections ahead. (But as Keynes said, in the long run we’re all dead.) Others see this contest as an emblematic last chance.

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Dan, once a south London councillor, was the spirit-raising call of the day – echoing many others: “I’m more hopeful about Labour than I’ve been in years! All the family, four generations, distant cousins, all joined to vote Keir. The election felt like the shock of 1992, the despair. But Labour recovered by 1997. I see a lot of hardcore Momentums, but those young idealistic ones are coming round to Keir, they want to win. My dad and sister voted Corbyn, but they’re voting Keir.”

The rift is so deep that some misguidedly yearn for a Starmer victory to purge Momentum from the party: that’s not the way, Starmer warns. The civil war has to end – his programme is a plan to unite not divide.

At the next desk was a man who quit the Liberal Democrats the day after December’s election, joining Labour to volunteer for Starmer. Nearby, the Labour peer Helena Kennedy paused from calling members to tell of her years in chambers when Starmer arrived as a pupil barrister: “He was the smartest by far, and we need clever. He has such good judgment, he’s courageous and decent through and through. He did so much pro bono work – for the miners, for Doreen Lawrence, for people beaten up in police stations and for disabled children’s benefits – that the head of chambers warned him he needed to do more paid work or he’d never get a mortgage.”

Her chambers urged him to apply to be director of public prosecutions: “We needed someone there with his values.” She talks of his template for dealing with domestic violence, training a cadre of prosecutors for sexual offences. Expect all of his past to be probed and attacked. Those trawling through his every decision as DPP often make wild accusations, misdating events before or after his time. The latest charge is over his unsurprising belief that benefit fraud, like tax evasion, should be prosecuted. But just wait for the Tory press to let fly if he wins: a Labour leader needs titanium armour-plating and he is more tested than most.

Most members I called spoke of his authority and gravitas, but whatever bookies think, a Starmer victory is not in the bag with an unpredictable electorate. Some said he’s short on jokes, but others that he’d be good at skewering Boris Johnson’s duff jocularity. Many looked forward to Starmer at the dispatch box with Labour’s great underused talent lined up behind him. This anarchic government has already lost a chancellor, has backbenchers threatening trouble and even its press backers are growling at No 10’s dictatorship. It’s ripe for challenge. None better than the grand prosecutor himself for a forensic demolition of Johnson/Dominic Cummings misrule. The stronger the vote for Starmer, the more Labour proves it is out of recovery and back on the frontline.

• Polly Toynbee is a Guardian columnist