Off a cliff they march: bowler hat-wearing, besuited Englishmen, left leg raised theatrically – à la Ministry of Silly Walks – over the precipice before they topple into the abyss. This was the front-cover image of the New Yorker sketched in the immediate aftermath of the 2016 Brexit referendum result, but it surely even better captures our current predicament. Sing it gently: It’s Beginning to Look a Lot Like No Deal.

Under Theresa May, this was always an empty threat, even though she paved its way with her inflammatory declaration that “no deal is better than a bad deal”. Under the clownish charlatan due to succeed her – drunk on rightwing populism, English nationalism, messianic delusion and Conservative existential angst – it is now a tangible possibility.

It may not happen. Boris Johnson isn’t really trusted by anyone – probably not even by himself – and the Brexiteer ultras are braced for another great betrayal. Perhaps he will risk their wrath by opting for an indefinite transition period. But a potential national emergency is just 104 days away – one that will lead to a humbled government clawing its way back to the negotiating table in an even more diminished position. And that’s why Labour, as a matter of urgency, must launch a nationwide all-out campaign against no deal.

All is not well with Team Labour. Brexit has sapped the morale of the grassroots, caused divisions at the top of the party, and led to a substantial chunk of its 2017 electoral coalition to defect – for now– to the Greens and Liberal Democrats. The Labour right scents blood, and – even as the hard right are in the ascendancy – plans to throttle the leadership and its allies. Writing in the Spectator, the journalist Isabel Hardman claimed: “Labour plotters are terrified that if they fail to act before an election they might end up with something even worse than a Boris Johnson victory: Corbyn himself becoming prime minister.” For any Labour MP to prefer what will be the most extreme Tory government in the era of universal suffrage over their own leader forming a government – well, what is there even to say?

Labour has pivoted to a pro-referendum-and-remain stance, but that’s insufficient: it hasn’t really built on it. As two leadership campaigns and a general election testify, Corbyn is best on the stump. He should position himself at the head of a national Stop No Deal movement, travelling the country and addressing mass rallies. Labour should call a national demonstration and organise local mobilisations in towns and cities. There should be billboards and dropdown banners splashed across urban landscapes; national and local media should be bombarded with Stop No Deal messaging, married to Labour’s referendum commitment. If – despite this week’s vote by MPs – Johnson manages to stop parliament sitting to ensure no deal, Labour must call it what it is, a coup d’état, and call for the people to occupy the House of Commons and demand an immediate general election. Labour should be clear: a national emergency beckons in the form of a ruinous exit from the EU fused with an ultra-Thatcherite assault on the economy, welfare state, and workers’ rights. It must be stopped.

Rather than just being a campaign against something, Labour should use such a movement to put its progressive domestic agenda front and centre, presenting it as a cure for the ills of austerity that led Britain to this crisis. It could be presented as a campaign to save industry, to appeal to swing voters in key seats, too.

Other than the Kate Hoey-type fringe, such a campaign would unite the party. Anti-Corbyn elements would still plot, but they would be marginalised and undermined. The magic of the 2017 election campaign would re-emerge, and those whose Brexit frustration has led them to leave the Labour fold would surely return. Whatever Johnson’s cabal claim, no deal is a minority position in the electorate: a majority coalition can be built against it. Plunging Britain into severe turmoil would look like an even riskier gamble by a Johnson administration.

In the aftermath of no deal, angry, traumatised remainers may end up venting their fury at Labour, too. This would be profoundly unfair: the party has consistently voted against the government’s Brexit plans and whipped its MPs twice to back a referendum, which has not passed for the simple reason that there is no majority in parliament for one. But politics is often about sentiments and emotion, not facts.

In the aftermath of a nationwide campaign against the folly of no deal, nobody would be able to claim Labour hadn’t given its all, and hopefully a disastrous outcome can be averted. A silly walk off a cliff beckons. Over to you, Labour.

• Owen Jones is a Guardian columnist