Who’s afraid of Jeremy Corbyn? Unthinking, knee-jerk Corbynphobia is a danger in the precarious weeks ahead, as the country’s fate hangs by that red thread. As parliament is brutishly banished by Boris Johnson after failing to secure an election, both sides retire to plot feverish ploys and counterploys for the Brexit endgame.

No-deal Brexit: cross-party rebel alliance gears up for clash with Johnson Read more

Johnson’s crew brief that they have scores of cunning loopholes to escape the paralysing parliamentary vice that stops him crashing the country out of the EU with no deal on 31 October, even defying the law. But the rebel alliance of opposition parties and Tory refugees is confident there is no trapdoor he can slip through without parliamentary consent.

That alliance has been remarkably solid – Labour, the SNP, the Liberal Democrats, Greens and Plaid Cymru, more used to battling over every seat – combining with the exiled Tories. Good grief, even with Philip Hammond, the demon austerity chancellor only weeks ago! Their unity of purpose and voting discipline was forged throughout the summer when they met, phoned and WhatsApped. Opposing a general election was a difficult hurdle for Corbyn: he, like all opposition leaders, called for one every day. (It’s said the absence of his strategy chief, Seumas Milne, on a prolonged holiday greatly eased the process of persuading the Labour leader: Milne and his coterie “bristle” at cooperation with other parties.) But the need to prevent Johnson calling an election across the Halloween tripwire date was paramount. The good sense of Keir Starmer, working with John McDonnell and Emily Thornberry, has nudged Corbyn a long way.

Parties must swallow their squeamishness and vote the Labour leader in if that’s ever required

But ahead lie many equally challenging tests of alliance unity. When parliament reconvenes in October it will have 12 days to close all loopholes and prevent a no-deal exit. Johnson may resign, or as a last resort Labour may need to depose him with a no-confidence vote. If so, the leader of the opposition would be called first to form an interim government; but will the alliance stomach him? When first mooted, the answer was no, but many are showing a new willingness to accept the inevitable.

Take Kenneth Clarke, the expelled former Tory chancellor. Asked which is worse, Corbyn or no-deal Brexit, he tells the Observer: “Both are awful prospects, but I think a no-deal Brexit could cause far more damage to our future economic success than Corbyn.” More astonishing is last week’s report “City warms to Corbyn” in the Telegraph (yes, the Telegraph!). Citibank and Deutsche Bank analysts say he is “now seen as the lesser of two evils”. His policies may be “market-unfriendly” but still preferable to the “permanent shock” of no-deal Brexit. “Fears” of Labour “may be overstated”.

Others need persuading: the Lib Dem leader, Jo Swinson, may be softening her “no way” stance. If not, she’ll lose the party’s reputation for pragmatic politics. Starmer says to exit the EU with no deal through squabbling would be unforgivable. It can’t and mustn’t happen. Understandably, Swinson fears that going into an election in November she may be attacked as a Corbyn stooge, but she’d never be forgiven if she let Britain crash out.

Parties must swallow their squeamishness and vote the Labour leader in if that’s ever required. To prefer some grandee risks breaking the unity and goodwill of the alliance. In any case, to be an interim prime minister in this broken-backed parliament is almost meaningless: Corbyn would only have permission to call an election or do whatever parliament required. He would be as powerless as Johnson to promote his party’s policies without majority backing: a no-confidence vote could remove him instantly.

The notion of Corbyn the bogeyman has taken on a life of its own, giving him the worst personal ratings ever of any opposition leader. Day in, day out, scare stories in the Sun and Mail stoke the terror. This week’s Sunday Times leader warns Tory rebels against allying with him: “Given the chance, his circle of Stalinists will eat them for lunch. The far left, once in power, does not surrender it easily.” The Mail on Sunday’s leader calls him “a doddering, ill-educated Marxist”. After a week that exposed the prime minister’s serial incapacities, they take fright: proroguing today saves Johnson from another PMQs humiliation at the hands of Corbyn.

Brexit party: Farage seeks election pact with Conservatives Read more

It’s no use wishing for another leader of the opposition: this is the one Labour has, and in this crisis he is now stepping up to the plate. His leadership of the alliance has been “collegiate”: he is the grownup, while Johnson breaks things. Theresa May lost her 20-point lead in the 2017 election; Johnson’s lead in the polls is about half that. Corbyn’s manifesto back then was highly popular and you can bet it will sell well again. He’s a good campaigner; Johnson may disappoint.

Polls reveal little. Even Rallings and Thrasher, granular analysts of every ward, say the coming election is “the most difficult to predict in a generation”. Pollsters expect another hung parliament. In all this volatility, Johnson is proving a dud so far and Labour could well be the biggest party, though an overall majority is near impossible – a settlement with alliance partners will be essential. So this progressive alliance must stick together, with informal pacts on seats to see off Johnson and Nigel Farage, who are likely to ally. To win, Labour needs a great push for tactical voting, as analysed by YouGov founder Peter Kellner. Stand alone and the Brexiters win.

Johnson’s chief adviser, Dominic Cummings, boasts that he’s winning the long game: that voters despising the SW1 palaver will punish the parties that stopped Brexit. He may be right, Johnson could win on a mere third of the vote. But here’s the even longer view: he would be in charge of his own calamitous no-deal crashout, and have no one else to blame. Winning would feel very like losing – no cake and no eating it.

• Polly Toynbee is a Guardian columnist