Rachel Reeves will need to find more than £40bn of tax rises or spending cuts in the autumn budget to meet her fiscal rules, a leading research institute has warned.

The National Institute of Economic and Social Research (NIESR) said the government would miss its rule, which stipulates that day to day spending should be covered by tax receipts, by £41.2bn in the fiscal year 2029-30.

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In its latest UK economic outlook, NIESR said: “This shortfall significantly increases the pressure on the chancellor to introduce substantial tax rises in the upcoming autumn budget if she hopes to remain compliant with her fiscal rules.”

The deteriorating fiscal picture was blamed on poor economic growth, higher than expected borrowing and a reversal in welfare cuts that could have saved the government £6.25bn.

Together they have created an “impossible trilemma”, NIESR said, with the chancellor simultaneously bound to her fiscal rules, spending commitments, and manifesto pledges that oppose tax hikes.

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The institute urged the government to build a larger fiscal buffer through moderate but sustained tax rises.

“This will help allay bond market fears about fiscal sustainability, which may in turn reduce borrowing costs,” it said.

“It will also help to reduce policy uncertainty, which can hit both business and consumer confidence.”

It said that money could be raised by reforms to council tax bands or, in a more radical approach, by replacing the whole council tax system with a land value tax.

To reduce spending pressures, NIESR called for a greater focus on reducing economic inactivity, which could bring down welfare spending.

Growth to remain sluggish

The report was released against the backdrop of poor growth, with the chancellor struggling to ignite the economy after two months of declining GDP.

The institute is forecasting modest economic growth of 1.3% in 2025 and 1.2% in 2026. That means Britain will rank mid-table among the G7 group of advanced economies.

‘Things are not looking good’

However, inflation is likely to remain persistent, with the consumer price index (CPI) likely to hit 3.5% in 2025 and around 3% by mid-2026. NIESR blamed sustained wage growth and higher government spending.

It said the Bank of England would cut interest rates twice this year and again at the beginning of next year, taking the rate from 4.25% to 3.5%.

Persistent inflation is also weighing on living standards: the poorest 10% of UK households saw their living standards fall by 1.3% in 2024-25 compared to the previous year, NIESR said. They are now 10% worse off than they were before the pandemic.

Professor Stephen Millard, deputy director for macroeconomics at NIESR, said the government faced tough choices ahead: “With growth at only 1.3% and inflation above target, things are not looking good for the chancellor, who will need to either raise taxes or reduce spending or both in the October budget.”