In the age of David Cameron and George Osborne, the left’s arguments seemed straightforward. Here was a slash-and-burn assault on the public realm, and an ideologically driven one at that.

Despite initial claims that an attempt to drive government spending back to 1930s levels was simply an unavoidable necessity to save Britain from the fate of Greece, Cameron would later admit the objective was a permanently “leaner” state. At the centrepiece was an onslaught against the welfare system that targeted disabled people and, over time, low-paid workers, accompanied by an unrelentingly vicious campaign to demonise benefit claimants.

In opposition, the Labour party failed to rebut the claims that overspending caused Britain’s post-crash plight

The project added a dash of social liberalism to the mix: Cameron cavorted with huskies and pledged to hug hoodies; although he would go on to savage “green crap”, and equal marriage was introduced without the support of most Tory MPs.

In opposition, the Labour party failed to rebut claims that overspending caused Britain’s post-crash plight; it was this position that sank the party in 2015. Outside Westminster, anti-austerity politics became the creed of the left and powered the subsequent Corbyn insurgency.

Five years on we live in a very different era, one a traumatised left has not yet computed. Boris Johnson and Dominic Cummings are proving to be able students of the new right, which blends a culture war on progressive social values with an unashamed raiding of both the rhetoric and substance of leftwing economic ideas. Poland’s ruling Law and Justice party synthesises a bitter opposition to LGBT rights, an anti-choice stance on abortion, and anti-migrant and anti-Muslim demagoguery with welfarism and so-called repolonisation, a process of nationalisation.

Hungary’s far-right regime revels in its hatred of foreigners and indulges in flagrant antisemitism, while imposing taxes on foreign-owned companies, forcing utilities to slash household bills and nationalising private pension funds. Donald Trump, too, vowed to rip up trade deals that hammer working-class Americans, rebuffed free traders with tariffs and pledged a huge infrastructure splurge.

Last year, Labour did not run against a prime minister contemptuously responding to struggling nurses with “there is no magic money tree”. The new masters of the Tory party instead set a cap on borrowing to invest at about 3% of GDP a year, allowing the figure to rise from £47bn to £70bn. Along with cycling routes, Johnson has committed to pump £5bn over half a decade into Britain’s crisis-ridden bus services, given HS2 the go-ahead and nationalised Northern Rail. Even current spending has been raised, with cuts to police numbers largely reversed, £34bn for the NHS and money invested in schools. Big caveats are needed here: the annual hike in NHS spending is about half the average of the New Labour years; most schools will be worse off than in 2015; and the Institute for Fiscal Studies points out a decade’s worth of Tory austerity is being baked in.

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As economist James Meadway put it to me: “The problem is, after a period of time of things getting worse, small improvements feel positive … In a desert, if someone offers you a glass of water, you think: fantastic.”

The left playing the same tunes – about Tory cutters and slashers – won’t work. Instead, other challenges need posing. Carys Roberts, executive director of the Institute for Public Policy Research, says that capital spending is necessary, but it is no substitute for spending on the decimated social infrastructure so many communities depend on. The actual amount of spending needs scrutinising too: while the Tories have given themselves an upper limit of 3% of GDP on capital investment, the manifesto plans only add up to 2.4%. “The government is shying away from the hard job of raising taxes on wealth that would make spending possible in a fairer way,” Roberts says.

There’s another important question: what is new spending achieving? Are the measurements simply rising trade and GDP growth, asks Alfie Stirling, chief economist at the New Economics Foundation, or is it to meet tangible progressive objectives such as reducing child poverty and carbon emissions? The climate emergency must be a key priority, both because it poses an existential threat to humanity and because tackling it offers the chance to build high-skilled industries with well-paid jobs.

And while market dogma promised freedom from an oppressive state, it bequeathed a legacy of insecurity for much of the working population. “Freedom is pretty meaningless if you don’t have the resources to be secure.” Stirling offers up reform of social care, cheaper housing and affordable public transport – and asks what vision the left currently has for social security and local government. Funding isn’t enough, either. As the James Meadway puts it: “We need to start talking about giving people control and ownership over assets and where they work.” The Brexit project promised to take back control – the very thing millions feel they lack over their lives.

Revealing the true nature of the Tories’ economic agenda will mean dismantling their rhetoric. The policy of free ports – low-regulation, low-tax zones – jars with other promises. When David Frost, Johnson’s chief EU negotiator, announces Britain’s refusal to commit to maintaining environmental, employment and social standards on a par with the EU, the Tory right’s dream of a race to the bottom menaces more than ever. The left must prepare to fight it. But the Johnson-Cummings axis has at least understood its constituency. Genuine enthusiasm for economic liberalism has never existed beyond a small sliver of the electorate.

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Polling shows that Tory voters support public ownership of rail, while a significant minority support nationalisation of water and energy, and raising taxes on the affluent. Many are also enthused by the so-called culture war – better known as baiting minorities and women over the rights they have won. That’s why Cummings says there will be no more “drivel” about “gender identity diversity blah blah”, why an adviser passionate about eugenics was hired, why the prime minister’s spokesman refused to say whether Johnson believed black people had lower IQs, and why anti-migrant sentiment is stoked. Here, the left must not concede an inch, or it will legitimise prejudices that not only menace minorities but shift the terms of debate on to Tory turf.

This new era means a vision that is ambitious and hopeful is more important than ever to the left. This is the challenge Labour’s next leader must confront.

• Owen Jones is a Guardian columnist