The reckless pledges of tax cuts by Conservative Party leadership contenders could transform the politics of tax and spend – but to Labour’s advantage, rather than the Tories.

The tax-cutting brigade, determined to halt the front-runner Rishi Sunak in his tracks, accuse him of being a “socialist”. Yet as they scramble for the votes of Tory MPs, they repeat a costly mistake the Tories traditionally accuse Labour of – making unfunded promises.

Their tax cuts, averaging £46bn a year at the latest count, would have to be funded by either spending cuts or higher borrowing but their campaign teams refuse to say which. There’s vague talk about our old friend efficiency savings. There’s little about spending pressures such as post-pandemic recovery in health and education or the dangerous new world and demographic time bomb that the Office for Budget Responsibility warned last week has put public debt on “an unsustainable path”.

Sunak is right to warn about “fairy tales”, insisting tax cuts must wait until inflation has been brought down. Of the other runners, only Kemi Badenoch has shown similar restraint, promising to eschew the “cakeism” of Boris Johnson.

Labour rightly senses an opening: from now on, shadow cabinet members believe the Tories will face the same “how will you pay for it?” question that normally haunts Labour. “The Tories usually get the benefit of the doubt from the media and the public, while we don’t. That will change now,” one Labour frontbencher told me.

Wishful thinking? No, I think Labour is on to something. Even if Sunak becomes prime minister – by no means certain – his cabinet will likely include at least some of those who have made rash pledges during the leadership election. For example, Nadhim Zahawi will be quizzed about his suggestion he will cut his departmental budget by 20 per cent. Labour will try to tar all Tories with the same “austerity or higher borrowing” brush.

“The tables have turned,” Rachel Reeves, the shadow chancellor, said in a speech on Wednesday. “Any lingering sense that the Conservatives are the party of economic responsibility has been shredded to pieces over the past few days. Instead of setting out serious plans to help people with the cost of living crisis, we are presented with the extraordinary spectacle of a Tory tombola of tax cuts – with no explanation of what public services will be cut, or how else they’d be paid for.”

To ram home the role reversal, Reeves took the opportunity to advertise Labour’s tough fiscal rules. Although Labour is often accused of having no policies, it has a more detailed economic plan than the Tories. The Johnson government talked about one but never produced it amid differences between the prime minister and chancellor Sunak.

The central aim of that plan must be to improve the UK’s woeful record on growth. Most economists argue that tax cuts would make only a marginal difference.  Reeves was speaking at the launch event for a book, Stagnation Nation, warning a toxic combination of low growth and high inequality has left typical UK families £8,800 poorer than their counterparts in the comparable countries of France, Germany, the Netherlands, Australia and Canada. The study is by the Resolution Foundation and Centre for Economic Performance at the London School of Economics.

Most of the Tory contenders are happier to talk about tax cuts than growth. In concentrating their fire on Sunak, rival camps risk trashing their party’s brand and record in the past 12 years. When Labour distanced itself from New Labour after its era ended in 2010, it was no surprise that voters turned away from the party. It is only recently that Keir Starmer has trumpeted New Labour’s successes in power.

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Sunak is perfectly within his rights to claim the mantle of Margaret Thatcher; she raised taxes in 1981 to balance the books before cutting them seven years later. As her then-chancellor Nigel Lawson wrote in his memoirs: “The notion that tax cuts, without any spending cuts or substitute source of revenue, will so stimulate the economy that the budget balance will improve ... is a spurious kind of virtuous circle and emphatically not part of my thinking.”

In their desperation to stop Sunak, Johnson’s allies accuse the former chancellor’s campaign of “dirty tricks” by switching some of its votes to Jeremy Hunt because they would rather face him in the run-off among Tory grassroots members.  That would be the same Johnson whose team “lent” Hunt votes in the 2019 leadership election to ensure he fought Hunt, a 2016 Remainer, rather than fellow Leaver Michael Gove in the shoot-out.

It is ludicrous to portray Sunak as a dangerous spendthrift left-winger. He was slow to help families struggling in the living standards crisis and less keen than Johnson on the “net zero” agenda. He has consistently voted for cuts in welfare spending. Sunak would keep the policy of sending asylum seekers to Rwanda and does not rule out scrapping the BBC licence fee or taking the UK out of the European Convention on Human Rights.

If he’s a socialist, I’m a banana.