The Bank will intervene in the bond market after a recent sell-off and surge in bond yields.
The plan will be "carried out on whatever scale is necessary" as it seeks to "restore orderly market conditions".
The Bank will step in to buy Government bonds – known as gilts – at an “urgent pace” after fears over the Government’s economic policies sent the pound tumbling and sparked a sell-off in the gilts market.
It comes after the IMF said it was “closely monitoring” developments in the UK and was in touch with the authorities, urging Chancellor Kwasi Kwarteng to “reevaluate the tax measures”.
In a statement, the Bank said: “Were dysfunction in this market to continue or worsen, there would be a material risk to UK financial stability.
Governor of the Bank of England Andrew Bailey Dan Kitwood
Chancellor of the Exchequer Kwasi Kwarteng leaves 11 Downing Street Aaron Chown
“This would lead to an unwarranted tightening of financing conditions and a reduction of the flow of credit to the real economy.
“In line with its financial stability objective, the Bank of England stands ready to restore market functioning and reduce any risks from contagion to credit conditions for UK households and businesses.
“To achieve this, the Bank will carry out temporary purchases of long-dated UK Government bonds from September 28. The purpose of these purchases will be to restore orderly market conditions.
“The purchases will be carried out on whatever scale is necessary to effect this outcome. The operation will be fully indemnified by HM Treasury.”
In response, the Treasury has said the Government will continue to “work closely” with the Bank.
A spokesperson said: “The Bank of England, in line with its financial stability objective, carefully monitors financial markets and any potential risk to the flow of credit to the real economy, and subsequent effects on UK households and businesses.
“Global financial markets have seen significant volatility in recent days. The Bank has identified a risk from recent dysfunction in gilt markets, so the Bank will temporarily carry out purchases of long-dated UK government bonds from today in order to restore orderly market conditions.
“These purchases will be strictly time-limited, and completed in the next two weeks. To enable the Bank to conduct this financial stability intervention, this operation has been fully indemnified by HM Treasury.
“The Chancellor is committed to the Bank of England’s independence. The Government will continue to work closely with the Bank in support of its financial stability and inflation objectives.”