Taxes must rise in the autumn if Chancellor Rachel Reeves is to meet her self-imposed borrowing rules, according to an economic thinktank.
The National Institute of Economic and Social Research (Niesr) said the government was on track to miss the target it has set itself by £41.2bn.
It recommended “a moderate but sustained increase in taxes” including reform of the council tax system to make up the shortfall.
The government said “the best way to strengthen public finances is by growing the economy”, but the Conservatives said Labour “always reaches for the tax rise lever”.
When she became chancellor, Reeves set out two rules for government borrowing, which is the difference between public spending and tax income.
The first rule was that day-to-day spending would be paid for with government revenue, which is mainly taxes. Borrowing can only be for investment.
The second rule was that debt must be falling as a share of national income by the end of a five-year period.
Reeves has repeatedly said these rules are “non-negotiable”.
The chancellor originally promised not to raise taxes further, but recently refused to rule it out after disappointing data on economic growth.
Stephen Millard, deputy director for macroeconomics at Niesr, said Reeves “will need to either raise taxes or reduce spending or both in the October Budget if she is to meet her fiscal rules”.
Niesr argues that raising taxes would help build a “buffer” that would reassure investors about the stability of the UK’s public finances.
That in turn “may reduce borrowing costs” for the government, it said.
Niesr said the £41bn shortfall in the government’s budget was in part due to weakening growth over the past few months, resulting in a lower tax take and higher government borrowing.
But the reversal of welfare cuts, which were originally designed to save £5.5bn a year by 2030, had also had an impact, it said.
The welfare cuts were watered down, following opposition from within the Labour Party, and are now expected to save less than half the original amount.
As a result the chancellor now faced a “trilemma”, the thinktank said, over which of her pledges to fulfill: meeting her spending commitments, her manifesto promises to avoid tax rises on working people, or meeting the limits she has set on borrowing.
One of these commitments will need to be dropped, Niesr concluded, but it said the government should prioritise protecting public expenditure that supports the most vulnerable, while also safeguarding public investment which supports future growth.
Niesr said the government’s other priority should be policies to promote growth and productivity, to boost living standards across the UK.
It said that the living standards of the poorest 10% of the population were now 10% lower than pre-Covid levels.
When Labour came to power a year ago, it said it wanted to make the UK the fastest growing country in the G7 group of nations.
However, the UK had faced trade policy uncertainty and geopolitical risk, as well as domestic challenges, the thinktank said.
Niesr said its analysis suggested the economy would grow “modestly” at 1.3% in 2025 and 1.2% in 2026, placing the UK in the middle of the G7 economies.
The IMF recently said it thought the UK was set to be the third fastest growing economy out the world’s so-called most advanced economies this year and the next, after US and Canada.
Niesr said inflation, the rate at which prices are rising, remained “stubborn” and would be 3.5% this year and 3% next year.
The thinktank, which is not affiliated to any political party or movement, did not suggest which taxes should rise or by how much.
However, it added that the government should also consider reducing welfare spending by speeding up plans to help people relying on benefits get into work.
The chancellor should also consider reforming council tax or even replacing it altogether with a land value tax, Niesr suggested.
A Treasury spokesperson said: “As set out in the plan for change, the best way to strengthen public finances is by growing the economy – which is our focus.”
However, shadow chancellor Sir Mel Stride accused Labour of not understanding the economy.
“Experts are warning Labour’s economic mismanagement has blown a black hole in the nation’s finances which will have to be filled with more tax rises – despite Rachel Reeves saying she wouldn’t be back for more taxes,” he added.