Government spending will increase to over £1 trillion a year by 2023/24, the Resolution Foundation has predicted.
It would be the first time in history that UK government spending rises above the £1 trillion barrier, according to the think tank's report.
The analysis compiled ahead of the 11 March Budget forecasts that the government will raise spending to about 40% of GDP by the end of the current parliament.
This would eclipse the spending of Tony Blair's New Labour governments and take Britain back to 1970s levels of spending.
However, the Resolution Foundation warns that the money for extra spending would probably require tax increases, unless Chancellor Rishi Sunak broke budget rules drawn up by his predecessor, Sajid Javid.
Commenting on the report, Jack Leslie, Economist at the Resolution Foundation, said: 'If the Chancellor wants to increase spending on day-to-day public services in a fiscally responsible way, he will have to change another of his party's traditional priorities – lower taxes.
'Higher spending will require higher taxes.'