Interest rates for new long-term government borrowing leapt to a 20-year high last month, after Kwarteng announced 45 billion pounds of unfunded tax cuts, on top of even greater short-term support for households' and businesses' energy bills.
"The Chancellor should not rely on over-optimistic growth forecasts or promises of unspecified spending cuts.
British government borrowing looks on course to hit 194 billion pounds this financial year and to still be 103 billion pounds in 2026/27 - 71 billion more than government forecasters predicted in March, the IFS said.
COSTLY DEBTDebt interest would cost 106 billion pounds this year and 103 billion pounds in 2023/24, the IFS predicted, due to the large amount of finance raised in years gone by through issuing bonds that pay interest that rises as inflation goes up.
"Such spending cuts could be done, but would be far from easy," the IFS said.