Prime Minister Liz Truss's "Growth Plan" is Britain's second roll of the dice at economic renewal following the 2016 vote for Brexit which, so far at least, has failed to yield returns.
Investors reacted with dismay to the combination of free spending, unfunded tax cuts and huge increases in government borrowing announced by finance minister Kwasi Kwarteng on Friday.
His statement marked a step change in British economic policy, harking back to the Thatcherite and Reaganomics doctrines of the 1980s that critics have derided as a return to "trickle down" theory.
The pound crashed below $1.09 for the first time since 1985 and British government bonds suffered the biggest daily fall in decades.
International observers looked on with bewilderment, even if business groups at home saw merit in many of the plans outlined by Kwarteng, who says low growth is the real gamble.
"I've rarely seen an economic policy that is as uniformly panned by economic experts and financial markets," said Harvard professor Jason Furman, former chair of the U.S. Council of Economic Advisers during Barack Obama's presidency.
"It shockingly came in below the low expectations that almost everyone had," he added.
Willem Buiter, a former Bank of England rate-setter and Citi's chief global economist until 2018, said Kwarteng's plans to ramp up borrowing were "totally, totally nuts".
"From a cyclical perspective it is, I think, a disaster," Buiter said, adding that he had no objection in principle to tax cuts for firms and households with a better fiscal balance.
"It's probably the epitome of casino macroeconomics," said Jacob Kirkegaard, nonresident senior fellow with the Washington- based Peterson Institute for International Economics think tank.
In Germany, the director of the German Council on Foreign Relations (DGAP) Guntram Wolff said Truss's plans amounted to a "Singapore-on-Thames" attempt to deregulate Britain's economy and boost the City of London.
"The economy has more than the City... It is no surprise that pound sterling has lost today," he said.
SLOWLY, THEN ALL AT ONCE
On Thursday Kwarteng said his plans to grow the economy would "build stronger capacity to alleviate inflationary pressure".
On Friday, those plans sparked a market meltdown that will only exacerbate inflation in the months, and possibly years ahead - automatically raising the bar for the eventual success of Kwarteng's plan.
U.S. investment bank Citi said sterling risked a confidence crisis among international investors.
"The risk now is that the UK government has diminished its credibility at one stroke, and you saw that with the market runoffs," said Dan Hamilton, nonresident senior fellow at the Brookings Institution, a U.S. think tank.
The collapse in investor sentiment leaves Bank of England Governor Andrew Bailey with a serious problem.
"Fiscal and monetary policy are now at war with each other in the UK," Furman said.
Hamilton agreed, adding that this tension was not evident in other major economies.
In financial markets, a small number of analysts predict that the BoE will be forced to raise interest rates before its next interest rate meeting.
"I think if you if you were Andrew Bailey and you were looking just at the detail of the market moves, you would already have called an emergency meeting," said Kirkegaard.
Buiter said he could think of few historical parallels for Britain's new fiscal approach, even if there were superficial similarities with the tax-cutting Thatcher years.
Britain's Institute for Fiscal Studies compared Kwarteng's statement to a budget in 1972 that similarly sought to double Britain's rate of economic growth, but is widely remembered as a disaster for its inflationary effect.
Furman doubted that Truss would be able to implement her plans before running into some economic hard truths, as happened to Ronald Reagan in the early 1980s.
The U.S. Republican president was forced to U-turn on a major tax-cutting drive as the U.S. Federal Reserve jacked up interest rates.
Furman said Truss might also have no choice but to undo some of her plans if Britain's debt problems start to spiral because of higher interest rates.
"Sometimes a country's hand is forced," he said.
($1 = 0.9111 pound)
(Reporting by Andy Bruce; editing by Jonathan Oatis)
By Andy Bruce and Lindsay Dunsmuir