U.S. lawmakers' rejection of a $700 billion (377 billion pound) financial bailout plan was "very disappointing," Prime Minister Gordon Brown said on Monday, according to Reuters.
The U.S. House of Representatives earlier voted against the plan to help the financial industry in a shock vote that sent global markets sliding.
"The vote in America is very disappointing," Brown told BBC television.
"We've obviously sent a message to the White House about the importance that we attach to taking decisive action in America."
Brown said he, Bank of England Governor Mervyn King and Chancellor Alistair Darling would "take whatever action is necessary to ensure the continued stability of the system."
Earlier on Monday, the government nationalised Bradford & Bingley, the second bank taken into public ownership this year as a deepening financial crisis claimed victims around the world.
Brown threw his support behind the U.S. bailout plan when he held talks with U.S. President George W. Bush in Washington last Friday.
Bush said after that meeting he had told Brown the plan was big enough to make a difference and he believed it would pass.
Conservative leader David Cameron reacted to the U.S. vote by saying the "eyes of the world are on Congress."
"A deal is needed in order to stabilise financial markets and financial institutions, not just in America but elsewhere," he told reporters.
He said the Conservatives were ready to help the British government "in any way that is necessary to help bring stability at what is a time of great anxiety."