Theresa May’s premiership has managed to stitch together a vast array of ignominies, blunders and self-inflicted calamities, but one of its most monumental failures has to be universal credit. At a time when Britain’s children have suffered the biggest jump in poverty for nearly three decades, its nationwide rollout will drive a substantial chunk of the population into hardship and poverty. Ministers know this, so it can only be described as a calculated act. If my predictions can easily be dismissed as leftist scaremongering, listen to the work and pensions secretary, Esther McVey.

Half of all single parents, she told the cabinet, and two-thirds of working-age couples with children are set to lose £2,400 a year. According to the Trussell Trust charity, in places where UC has been fully rolled out, food bank use has jumped by over half. UC recipients report going hungry, and being left unable to buy clothes or toiletries or pay for heating, and struggling to pay rent. Why does mass hardship beckon? Because an often inaccessible system riddled with complexities and delays is colliding with £12bn of benefit cuts. Have no doubt: this is impoverishment by design.

That’s why Gordon Brown is right to warn of “a return to poll tax-style chaos in a summer of discontent”. Thatcherism imposed the poll tax at a time of hubris. The Tories had just won their third landslide victory. They had a majority more than 100 seats. Thatcher appeared the master of all before her. And yet the anti-poll tax movement mobilised mass demonstrations, while millions engaged in an act of unprecedented mass civil disobedience: refusing to pay. The movement fatally wounded an apparently unassailable prime minister and, along with divisions over Europe, abruptly terminated her reign.

Today the Tories are, arguably, more divided than at any point since the Corn Laws, in the first half of the 19th century. Their leader remains in place only because of internal paralysis. They are losing the battle of ideas on every front to a resurgent, confident opposition. A radical left that passionately believes in extra-parliamentary action is now stronger than at any point in British history. Momentum is uniquely well suited to launch a mass campaign against universal credit. Their innovative campaigning – from mobilising activists to crafting viral videos watched by millions of voters – helped swing last year’s elections.So far, it has been focused on Labour’s internal machinations; that must now surely change.

In the late 1980s, an All-Britain Anti-Poll Tax Federation was established, bringing together local groups across the country to coordinate action. A similar movement focused on UC must now be founded to prepare for the mass protests and civil disobedience that must be the response to a deliberate Tory attempt to drive millions into hardship. Next July, an additional 3 million families are set to be forced on to UC: they are largely unaware of what is about to befall them. A new movement must be prepared now for the deluge.

Such a movement must have a wider function, too. It was George Osborne’s strategy in particular to demonise social security and its claimants, and it was frighteningly effective. As well as diverting anger at stagnating living standards towards the wrong targets, it had another desirable consequence. The Tories wished to portray Labour’s fictional overspending as the root of Britain’s economic malaise: and that spending was portrayed as being frittered away on the undeserving. But this campaign has lost its salience, partly because Labour now refuses to indulge it and instead emphasises deserving targets of anger, like bankers and tax cheats. Along with the failures of austerity, that is surely one reason why support for higher tax and spending is at a 15-year high. John McDonnell has rightly called for UC to be scrapped, but Labour is committed to reversing only a fraction of Osborne’s devastating cuts. It privately points out that rebalancing the economy away from low pay and high rents will reduce social need, automatically reducing social security spending. That is right, but there will be a gap between this restructuring and the impact of the cuts, and millions risk falling into it. Labour’s current position is simply not good enough. Some of its disingenuous critics argue that Labour is frittering money on “middle-class” students that could be used to reverse such cuts.

These critics were often the same individuals who claimed the Labour left could never win over so-called middle England, and who cheered on Labour politicians who demanded tougher clampdowns on benefits. Labour can only win as a coalition of low- and middle income earners – and young people, who have been hammered by a housing crisis, student debt, job insecurity and services being scrapped, desperately need help. It’s not either-or: the wealthiest Britons more than doubled their fortunes after the crash.

Labour should be pressured to even more radically raise taxes for the highest earners and the wealthiest to reverse all benefit cuts. Social security spending, after all, will automatically fall as living standards rise and the housing crisis subsides. A standard narrative has been that the gravest threat to the government is Brexit. But it may well be that this class war being waged proves the Conservatives’ undoing. They were defeated when they were at their strongest in government. They can surely be defeated when at their weakest.

• Owen Jones is a Guardian columnist