Rishi Sunak last night claimed he must whack up taxes and slash public spending or the economy will be plunged into chaos again.
The PM warned the financial markets will punish Britain unless the Tory government unveils a brutal Autumn Statement this week.
Speaking to journalists as he flew to Indonesia for the G20 summit, Mr Sunak was challenged about concerns his plan will choke off economic growth.
But he insisted the country will be battered by international investors unless he takes a tough approach.
He said: "Financial conditions in the UK have stabilised clearly, but they have stabilised because people expect the government to take the decisions that will put our public finances on a sustainable trajectory
"It's the government's job to deliver on that and that's what the Chancellor will do."
The PM said it was "crucial" to deliver on "the expectations of international markets".
Asked whether the country is in for years of pain, Mr Sunak insisted he wanted to "lay the foundations for the economy to recover and grow".
"Ultimately, that's what we all want to see," he added. "That's how we're going to be able to cut people's taxes over time and support public services."
It comes as Joe Biden will also tell the Prime Minister to finally end the Brexit rows over Northern Ireland as they meet for the first time this week.
Downing Street last night said the President and PM will renew the “strong alliance” of Britain and the US, which “will not change”.
But Mr Biden is expected to urge Mr Sunak to resolve the dispute with the EU over Northern Ireland in time for the 25th anniversary of the Good Friday Agreement next April.
The G20 summit in Bali will be the first time a British PM has met a representative of the Russian government since the invasion of Ukraine.
Vladimir Putin has chosen not to attend the event and will send his foreign minister Sergei Lavrov instead.
No10 has pledged that Mr Sunak will “absolutely use every opportunity to confront Russia about its continued illegal actions”.
“We will not shy away from any opportunity to make our position loud and clear,” the PM’s spokesman said.
Mr Sunak will call on Moscow to allow grain shipments out of Ukraine to continue as it threatens to stop them from this Saturday (19).
The PM will also urge fellow world leaders to maintain support for Volodymyr Zelensky. “[He] is emphatic that [our] support will not fade or alter and that we are in this for the long haul,” his spokesman said.
The leaders of the G20, which is made up of 19 nations and the EU, first met in 2008 in the wake of the financial crisis.
At the meeting, Mr Sunak will signal he will bring a halt to widespread economic intervention as he argues countries should “direct government support to where it’s most needed”.
The Prime Minister last night said: “Later this week the Autumn Statement will set out how we will get this country on the right path, put public finances on a stable footing and get debt falling.
“Creating a stable international system that protects the most vulnerable will be a core part of that work.
“But addressing the biggest economic crisis in a decade will require a concerted effort by the world’s largest economies – these are not problems we can solve alone. At the G20, leaders need to step up to fix the weaknesses in the international economic system which Putin has exploited for years.”
The members of the G20 are Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, Mexico, Russia, Saudi Arabia, South Africa, South Korea, Turkey, the UK, the US, as well as the EU.
