The plan by Prime Minister Liz Truss to slash taxes to boost growth has been described as an economic gamble.
A leading think tank is warning on the eve of the mini-Budget that the tax-cutting move will put Britain's debt pile on an "unsustainable" path that will add £100billion-a-year to public borrowing.
The Institute for Fiscal Studies (IFS) said a combination of higher spending and tax cuts championed by the Prime Minister would see the national debt balloon - even after the Government stops subsidising household energy bills.
It also suggested that it would be a "miracle" if the UK achieved a parallel increase in growth that ensured the economy grew faster than the debt burden.
Reversing April's 1.25% increase in National Insurance and cancelling next year's Corporation Tax rise will add around £30billion to the annual deficit alone, the IFS told the Telegraph.
With debt on an "ever-rising path", the IFS said future governments were likely to be forced into a renewed period of austerity to control the UK's debt mountain.
Tax burden
The IFS also warned that, even taking into account planned tax cuts, the tax burden would remain at the highest sustained level seen in the UK, because of flagging growth.
It said that boosting the economy would require a "concerted change in policy direction", including widespread tax reforms, tearing up planning laws and increased investment in education and infrastructure.
Chancellor Kwasi Kwarteng wants to target a long-term growth rate of 2.5%. The IFS said it would take time to permanently boost the economy.
"While we would get to enjoy lower taxes now, ever-increasing debt would eventually prove unsustainable," said Carl Emmerson, deputy director at the IFS.
"The increase in annual growth required just to stabilise debt as a fraction of national income under our forecasts would be equivalent to the difference in the growth seen over the quarter of a century between 1983 and the financial crisis in 2008 and that seen over the 2010s.
"Getting that scale of increase in trend growth, while not impossible, would require either a great deal of luck over a long period or a concerted change in policy direction. One cannot simply assume oneself to fiscal sustainability."
Taking action
A spokesman for the Treasury told the Telegraph: "In the face of soaring energy prices caused by Putin's aggression in Ukraine, it is absolutely right that the Government takes action now to help families and businesses, just as we did during the pandemic. Without urgent support, the alternative would have been unthinkable.
"However, the Government is committed to getting debt down in the medium term, and will update on how we will do in due course. And the Government's Growth Plan, which the Chancellor will unveil on Friday, will support sustainable public finances by ensuring the economy grows faster than our debt."
Also in tomorrow's mini-Budget, Chancellor Kwasi Kwarteng is to unveil plans under which more than 100,000 part-time workers will risk having their benefits cut if they do not agree to work longer hours.
Anyone who works fewer than 15 hours per week on the National Living Wage will have to attend coaching sessions at job centres and prove they are trying to increase their earnings.
The Chancellor described it as a "win-win" policy because it will help fill the 1.2million vacancies in the jobs market as well as helping those on low incomes to earn more by giving them intensive support with seeking work.
Mr Kwarteng will also announce extra support for over-50s to get back into work, as employment rates in that age group remain below pre-pandemic levels.