Difficult decisions will be needed "across the board" on tax and spending, the new chancellor has told the BBC.
Speaking in his first interviews since becoming chancellor, Jeremy Hunt said some taxes will go up, while government spending may need to fall.
Cutting the top rate of tax and not independently costing measures were mistakes being "put right", he added.
He also insisted he had a "clean slate" after Liz Truss sacked Kwasi Kwarteng on Friday.
Mr Hunt, a former foreign secretary who had not been part of Ms Truss's cabinet, was made chancellor on Friday as the prime minister sought to restore confidence in her government.
In another dramatic day in Westminster, the PM also scrapped the plan to freeze corporation tax - set out in the 23 September mini-budget - in another major U-turn.
Speaking to the BBC, Mr Hunt signalled a big shift away from the economic policies of Ms Truss and Mr Kwarteng.
"Taxes are not going to come down by as much as people hoped, and some taxes will have to go up," he said. "I'm going to be asking all government departments to find additional efficiency savings."
While he did not say where taxes could rise or public spending be reduced, Mr Hunt did not rule out cuts to NHS spending or rowing back on Ms Truss's pledge to increase defence spending to 3% of GDP.
The chancellor, a Rishi Sunak supporter in the leadership contest, said the government needed to "show the world we have a plan that adds up financially".
https://www.bbc.co.uk/news/uk-63268238