Pensioners and the wealthy could be the target of tax increases at Rachel Reeves’s autumn budget if the drastically worsening economic backdrop fails to improve, the Institute for Fiscal Studies (IFS) has said.

After the chancellor’s spring statement featured deep cuts to welfare to meet her fiscal targets, the UK’s leading experts on the public finances said Reeves could be forced to come back later this year with tax rises.

Paul Johnson, the IFS director, said a “risky and changing world – as President Trump’s actions overnight on tariffs demonstrate all too well” showed that Reeves’s policies were already in danger of becoming out of date.

“There is a good chance that economic and fiscal forecasts will deteriorate significantly between now and an autumn budget,” he said. “If so, she will need to come back for more, which will likely mean raising taxes even further.”

In a politically charged statement to the Commons on Wednesday, the chancellor announced a £14bn package of measures to rebuild £9.9bn of headroom against her self-imposed fiscal rules, after a sharp deterioration in the public finances since the autumn.

It comes after a sharp rise in government borrowing costs on global markets, reflecting domestic factors but also Donald Trump’s policies which have threatened to hit global growth and reignite inflation. Without the chancellor’s spring statement measures, the Office for Budget Responsibility (OBR) said it would have forecast a £4.1bn deficit against Reeves’s main fiscal rule, which requires day-to-day spending to be matched by tax receipts.

However, Johnson warned the economic outlook was evolving rapidly, and that Reeves had left a historically slim margin of headroom against her rules which could be quickly erased.

“That risks months of speculation over what those tax rises might be – a raid on pensions, a wealth tax on the richest, another hike to capital gains tax?

“I mention those not to commend them, far from it, but to exemplify the kinds of taxes regarding which mere speculation about increases can cause economic harm. With no sense of a tax strategy, we have no idea which way the chancellor might turn,” he said.

The OBR said on Wednesday that its worst-case scenario for escalation in Trump’s trade war could wipe out the chancellor’s headroom entirely. As if to underline the uncertain outlook, Trump announced a punitive 25% tariff on all car imports to the US just hours after Reeves spoke.

As well as committing to “non-negotiable” fiscal rules – limiting the capacity for additional government borrowing – Labour pledged before the general election not to increase income tax, VAT or national insurance, and to hold the main rate of corporation tax on business profits at 25%.

Johnson said a fresh round of cuts would be difficult to make because Reeves was about to set out her plans in the June spending review, which would be tough to renegotiate. Further changes to welfare – after a political backlash to the spring statement plans – would also be challenging.

He said the “easiest” option for Reeves would be to extend a freeze on the personal allowances for income tax and national insurance, which could raise about £10bn for the Treasury.

Pensions could also be targeted, while capital gains tax could be reformed, which would affect wealthier individuals most.

“One of the reasons I worry about pensions taxation is it looks like a nice juicy place to go for a lot of money,” he said.

Highlighting speculation before the October budget, Johnson said that rumours about pensions taxation led individuals to make changes to their personal affairs – even though the chancellor did not follow through on them.

“Given that she didn’t do anything back in that budget, I really wish the chancellor had said ‘and I am not going to do anything for the rest of this parliament’, so I suspect we will have that speculation again.”