In addition to the plunge in the value of the pound, it has also seen investors demand a greater rate of return for UK government bonds – essentially IOUs.
That is because the level of borrowing required to fund the government giveaway, including tax cuts and energy aid for households and businesses, shocked the market, which immediately questioned the sustainability of public finances.
The Lib Dems and SNP have also demanded a recall of parliament, while a growing number of Tory MPs have been criticising the government’s economic plans.
Simon Hoare, Tory MP for North Dorset and chair of the Northern Ireland Select Committee, said: “In the words of Norman Lamont on Black Wednesday: ‘Today has been a very difficult day’.
“These are not circumstances beyond the control of Govt/Treasury. They were authored there. This inept madness cannot go on.”
Meanwhile, a former minister told Sky News that there is a “growing movement” for Chancellor Kwasi Kwarteng to step down.
“The mainstream majority think we have crossed the Rubicon,” they said.
But another former minister tried to pour water on the flames.
They said: “It is inevitable the markets would react to a changing direction in economic policy. They will settle.”
Mr Kwarteng held a meeting with investment bankers this morning to try to reassure them.
He said he was committed to “fiscal discipline”, and that he was working closely with the Bank’s governor and the Office for Budget Responsibility.