Ahead of the new government’s first budget on October 30, chancellor Rachel Reeves has revealed her determination to change borrowing rules that will allow her to boost investment spending.

The overriding goal of the government is to promote economic growth, after more than a decade of stagnation in living standards. In the long run, boosting growth will produce more money for the government to improve public services. But while Reeves has given a strong steer as to how she will fund the public investment needed to grow the economy in the long term, she will also have to find money for urgent improvements to struggling public services like the NHS, a key election pledge.

There are three ways that the government can raise the funds it needs to boost investment and improve key public services. It can raise taxes, increase borrowing, or make cuts to spending. Given the scale of the challenge faced by the chancellor, all three are likely.

The government had made a rod for its own back with two of its key election pledges: not to raise the main taxes (income tax, national insurance, and VAT) on “working people”, while sticking to a set of fiscal rules that set strict limits on government borrowing. These pledges were designed to appeal to voters hit by the cost of living, while demonstrating to financial markets that Labour would be cautious with public money. Government borrowing reached nearly £80 billion in last six months, the third highest sum on record.

With the so-called financial “black hole” now estimated at £40 billion, not the £22 billion announced in July, the Treasury will need major tax rises that go well beyond the modest proposals from the election campaign. Although Labour may make some limited increases in other taxes on wealth, such as capital gains tax, this alone will not close the revenue gap.

The most likely candidate to bridge the gap is an increase in employer national insurance (NI) contributions, for example by making employers pay NI on their pension contributions. This could raise more than £15 billion per year. Reeves and prime minister Keir Starmer argue that this would not breach their manifesto commitments – but it will be politically controversial. Observers, including the Office for Budget Responsibility (OBR) and the Institute for Fiscal Studies, argue that such taxes are eventually felt by workers through either lower wages or staff cuts.

Further spending cuts are also on the cards. In July the chancellor announced a series of cuts, cancelling planned spending on the reform of social care, withdrawing the winter fuel payment to most pensioners, and ordering departments to make efficiency savings to help fund pay awards.

Other than for the NHS, Reeves is expected to squeeze spending in “unprotected” departments (prisons and local government, for example). On welfare spending, the Treasury has the rising bill for disability and incapacity benefits in its sights.

But even these decisions leave the government with a major funding dilemma. How will it pay for capital spending, everything from new hospitals and schools to roads, bridges and other infrastructure? All are key to boosting long-term growth.

While one of Reeves’ fiscal rules aims to ensure that day-to-day spending must be balanced by tax receipts (leading to the need for tax increases), borrowing for long-term public investment is not part of that calculation. But any increased borrowing for investment appears to be sharply curtailed by another fiscal rule, which says that total government debt (including that incurred by borrowing to invest) as a percentage of GDP must be falling within five years.

New government, new rules?

Despite Labour’s embrace of both these tight fiscal rules during the election campaign, the chancellor has now confirmed that she wants to modify this debt rule to allow herself to borrow more.

She plans to change how overall government debt is measured, effectively redefining it by including more government assets to set against the amount being borrowed. The likely new measure, known as “public sector net financial assets”, would include assets like funded local government pension schemes and student loans income, as well as government-owned companies like Great British Energy.

This could give the chancellor up to £50 billion in extra borrowing power for public investment. Her argument is that borrowing to build infrastructure gives the government a tangible asset that will pay for itself in the long term by boosting growth and tax receipts.

The government’s spending watchdog, the OBR, agrees that in the long term, well-planned public sector investment could benefit the economy, although it says it would take a long time to materialise. Many observers, including the former head of the civil service, Gus O'Donnell, and Mark Carney, the former governor of the Bank of England, strongly support increased public investment as a way to boost lagging productivity.

But there are risks in this strategy if it unsettles financial markets. Total government debt on the current measure now stands at £2.6 trillion, nearly the same size as the whole UK economy. It is costing the Treasury around £74 billion a year in interest payments, almost the size of the education budget.

If the bond markets (which buy government debt) take fright, they could force up the cost of borrowing further, which could raise interest rates on mortgages and other consumer borrowing. And news of the chancellor’s plan to change to the fiscal rule did cause bond yields to rise slightly. This suggests if government debt rises too rapidly, even within the new rules, this could have a destabilising effect. So the chancellor will have to judge carefully how much of the extra headroom she should use.

Like all Labour chancellors, Reeves faces the task of keeping both voters and the financial markets happy at the same time. Her strategy could end up alienating rather than pleasing both sides.

Given the scale of Labour’s ambitions, balanced against her limited resources, she may have little choice but to take such a bold approach. But her path between alienating business and disillusioning the public is a narrow one. And the longer it takes for her strategy to bear fruit in terms of a better standard of living and improved public services, the more difficult things will become politically.