What we’ve heard so far about the Budget sounds pretty austere, but the Chancellor defines austerity as a real reduction in government spending. It appears that ministries will receive supplements to cope with the rising cost of services.

The compromises in his budget are driven by his new fiscal rules. A new rule governing borrowing for investment, the ‘investment rule’ will replace the old debt rule, helping to reverse a planned £20 billion cut in spending on major investment projects. The new, broader measure of debt must decline within five years. But it is the new “stability rule” which will be the binding constraint on Wednesday. All daily expenditure of ministries, in terms of social assistance and debt interest, will have to be financed by tax revenues over a certain, as yet undetermined, period. This could be a really strict rule, much stricter than that of the Conservatives. The loan will only be used to invest.

Together, these two rules will define not only this budget, but the next half-decade, affecting every penny the government spends. Labor has calculated that its overwhelming majority is rooted in the public’s desire to address underperforming public services, such as the NHS, and in the decline in the quality of the public realm, from transport to city centers to to housing. According to this vision, the real “black hole” lies in public services. The “fiscal fiction” of unrealistic spending plans will become fiscal reality.

By demanding that spending gaps be filled with significant tax increases, the strategy here is to communicate an overwhelming tolerance for political pain to the markets that lend money to the Treasury. Essentially, a massive majority will be used to credibly secure surpluses on “current” spending. Some taxes will increase, but the bottom line is that this should help keep interest rates low for households, businesses and the government itself.

As a prominent central banker said on the sidelines of the IMF meeting, what is important in terms of market credibility is not just the amount of borrowing, but also the consistency of history and strategy around this loan.

A new chancellor must establish financial credibility. After all, it is common knowledge that credibility is hard to gain and much easier to lose. That’s the purpose of these self-imposed rules. But in recent years, chancellors have also had political credibility problems. More than one of them had been in office too short a time to even have an official budget. This is not a certainty given that all budgetary measures will actually be adopted by a rebellious and undisciplined ruling party. Across the Channel, this is precisely the problem in France, where Reeves’ counterpart, Antoine Armand, must convince that he can indeed adopt tough measures as a minority government. Rachel Reeves has no such problems.

Indeed, during an event in Washington addressing bankers, members of Congress and senators at the British ambassador’s residence, the chancellor had a moment of reflection. Exactly two years before, Kwarteng had delivered the same speech, against a backdrop of widespread mini-fiscal turmoil, including jokes about his shared role with Isaac Newton in resolving a historic sterling crisis. Following the Kwarteng “fiscal event”, members of the boards of UK clearing banks had to reassure their counterparties that Britain was “fine”. Finance ministers from developing countries were making the same half-joke about Britain, the old master, now the economy in crisis.

For a chancellor who, twenty years ago, was seconded to the British embassy as an economist, during one of Argentina’s debt crises, this was anathema.

That’s why, on Thursday morning, she and her team expect some anger from the richest taxpayers and bad headlines in some newspapers. But the flip side will be relief for users from the difficulties of many public services, and in particular what the Treasury hopes will be tranquil financial markets as it embarks on a long-term program of long-delayed investment in Britain’s economic future.

This is a budget that will be unpacked and dissected for months, if not years.