This is going to be an ugly weekend for British politics. How ugly we won’t quite know until Saturday night, when enough votes will have been counted to judge whether Keir Starmer’s government has suffered merely a midterm kicking or a full-blown collapse, and what dark forces may have been unleashed in the process. For you needn’t be a Labour voter to worry about the implications of local elections in which so many candidates were caught expressing views so extreme they chill the blood.

It’s fear of what this means for Britain in the long term that explains, in part, why the prime minister’s enemies were gathering long before the polling stations closed.

Angela Rayner is expected to make “an intervention” this weekend. Wes Streeting – the preferred pick of many ministers, if not party members – is said to have an entire shadow operation ready to go. Next week, the soft-left Mainstream grouping will publish what looks uncannily like the beginnings of a manifesto for Andy Burnham, via a report on “Manchesterism” and how the mayor’s economic experiment could be translated nationally. Though Starmer is visibly digging in, the idea of him leading the party into another general election seems vanishingly unlikely, meaning there will surely be calls this weekend just to get the inevitable over with.

Yet to trigger a leadership contest right now would be a mistake, and not just because some of Labour’s potential players aren’t even on the pitch yet. (You don’t have to be a paid-up Burnham fan to think he should be given time to try to get back into parliament, if only because otherwise he will for ever be Labour’s martyred king over the water. While a swift and uncontested coronation may look appealingly clean and quick, in retrospect it was doing Gordon Brown no favours by 2009, and a full-length leadership contest would have been a useful stress test for Theresa May in 2016.) The better reason for hesitating before pressing the nuclear button is to guard against the whole thing blowing up in Labour’s face.

What is their answer if Nigel Farage and Zack Polanski respond to a leadership contest – as they would be mad not to – by demanding a general election, accusing Labour of clinging illegitimately to power by imposing a new and unelected leader over the people’s heads? What if Farage whips the more riot-prone parts of his fanbase into a fury at the very idea of a squatter prime minister, most likely one to the left of the one they already hate? Though governments shouldn’t be held hostage by their opponents, to rerun the kind of infuriatingly exclusive process by which a tiny group of Tory members repeatedly changed leaders mid-parliament – and repeatedly got it wrong – in the current climate would be madness. The 99% of Britons who aren’t paid-up party members, and therefore not entitled to a vote, need somehow to be brought into the room.

Whoever leads Labour and Britain through the next three years may have to navigate a recession, or even a war, all while somehow conjuring up the sunny change for the better that millions were promised in 2024. They will need to tackle the cost of living while raising billions more for defence – which most likely means finding a way around manifesto promises on tax – and simultaneously convincing the bond markets that Britain isn’t bust. And in their nonexistent spare time, they will somehow have to try to bring an angrily polarised country together. To be blunt, none of the current contenders look entirely ready, but nor does the current prime minister. As the party entrusted nearly two years ago with power, Labour has a moral duty now to resolve that conundrum. If it chooses to do so by bundling a democratically elected prime minister out of the door – either via the kind of more or less consensual months-long transition agreed through gritted teeth by Tony Blair in 2006-7, or more brutally – then what follows must be a genuine contest geared for once to the actual job.

Having chaired Labour leadership hustings in 2010 and 2015, all I can say is that never has the current format – in which candidates traipse around the country trying to deliver clips for social media, while members dwell lovingly on big-picture ideas such as international diplomacy at the expense of things voters often care more about – seemed less fit for purpose. Across all parties, leadership contests have become a perfect test of candidates’ ability to find their own side’s erogenous zones while somehow failing to ask the questions that in retrospect mattered.

How exactly do the candidates make decisions? For that’s what being prime minister consists of, more than anything else: judgment call after judgment call on dilemmas escalated to No 10 precisely because they’re too big or bitterly contested to be resolved by anyone else. (Too late we discovered that Starmer doesn’t seem actually to enjoy taking political decisions; that May relied alarmingly heavily on her chiefs of staff; that Boris Johnson tended just to agree with whoever he was talking to at the time, leaving a trail of chaos in his wake.)

What do parliamentary colleagues who see them up close daily know that the rest of us should? (Tory MPs did their best to raise the alarm in 2022 about Liz Truss, but Tory members didn’t want to hear it – a mistake their Labour counterparts should beware repeating.) Do they actually know what they’re talking about, deep down? You would learn more from 10 minutes of each candidate being publicly and remorselessly grilled on economic policy by Brown, say, than in weeks of hustings. And, crucially, can they convince the overwhelming majority who currently say they wouldn’t vote Labour at least to give them a chance to put things right? For if not, pressure for an early general election will soon become overwhelming. Though US-style open primaries may be a step too far for the Labour party, holding public events open to all-comers on top of more traditional hustings for voting members would be a far better test of how prospective leaders handle hostile voters – and perhaps the beginnings of building a mandate.

All of this would take time to organise and, by the end of this weekend, perhaps Labour MPs may have concluded it’s time that they don’t have. But if so, they must remember that they won’t just be auditioning a leader for their own party: they will be choosing a prime minister for the country. Spin that roulette wheel too soon, and it isn’t going to land on red.

• Gaby Hinsliff is a Guardian columnist

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