London: Bank shares tumbled on the London stock exchange Tuesday following the rejection by the US House of Representatives of the massive US bail-out plan.

London's FTSE 100 Index slumped by 2.3 percent to 4705.5 points, its lowest level since December, 2004, as the shares of leading banks fell sharply.

Prime Minister Gordon Brown late Monday called the failure of Congress to adopt the plan as "very disappointing", but pledged that he would do "whatever is necessary" to protect Britain's financial system.

"The vote in America is very disappointing," said Brown. "The governor of the Bank of England, the chancellor and I will take whatever action necessary to ensure continued stability for Britain."

The opposition Conservatives pledged to cooperate with the government in the current crisis.

"We are a responsible opposition, we stand ready to work with the government and help the government in any way that is necessary to bring stability at what is a time of great anxiety," said its leader, David Cameron.