LONDON – Prime Minister Gordon Brown summoned the head of Britain's central bank and chief financial regulator for talks Tuesday after banks' share prices plunged amid investors' worries that the government hasn't done enough to strengthen bank balance sheets.

Brown and Treasury chief Alistair Darling held a meeting with Bank of England governor Mervyn King and Financial Services Authority chairman Adair Turner to consider possible new action to stabilize the country's financial system. After the session Darling promised to make a statement before markets opened Wednesday but he offered no details.

The BBC reported late Tuesday that the British government was poised to announce a rescue package for banking system. It reported the package would include a proposal to inject capital into banks and to provide a standby facility to ensure banks have enough cash to fund their day to day operations.

Shares in the Royal Bank of Scotland Group PLC, whose credit rating was downgraded by Standard & Poor's credit agency on Monday, plummeted by 39 percent to close at 90 pence ($1.58) on Tuesday in London.

RBS is one of the top 10 banking groups in the United States. It owns Citizens Financial Group Inc., a $161 billion commercial bank holding company, which has more than 24,000 employees and 1,600 branches, mainly in the Northeast and in Illinois, Indiana, Michigan and Ohio.

HBOS PLC closed down 41.5 percent at 94 pence ($1.65), Lloyds TSB Group PLC dropped 13 percent to 225 pence ($3.96) and Barclays PLC fell 9 percent to 285 pence ($5.01).

The share declines followed a meeting on Monday between the government's leading financial figures and the heads of Britain's biggest banks, during which they discussed a possible rescue plan for the beleaguered banking sector, according to two banking officials with knowledge of the meeting who asked not to be identified because the meeting was confidential.

Darling, King and Turner met with heads of RBS, Barclays and Lloyds to discuss the possibility of the government investing as much as 50 billion pounds ($87 billion) in the country's banks in order to shore up their balance sheets and restore confidence in the institutions, the banking officials said. The taxpayer money would buy the government large equity stakes in the banks.

But the two people familiar with the meeting said the government did not give details of exactly how much it would invest or when the proposed plan might come into effect.

“The Chancellor's delay in coming up with a plan is being interpreted as dithering,” said Labour lawmaker John McDonnell.

Shares at every major British bank – with the exception of HSBC Holdings PLC, which is known to have a relatively strong balance sheet – began falling soon after the London Stock Exchange opened on Tuesday morning, as investors searched for a detailed sign that Britain's banks were safe investments, despite the worsening global financial turmoil.

“Bond investors won't buy bank debt anymore, but those same bond investors are keen to buy government debt,” said Simon Maughan, a London-based analyst at MF Global Securities. “The thing the government needs to do is – short of nationalization – to close the perception gap between how bank and government debt is perceived.”

Buying large equity stakes in banks would be an obvious way the government could accomplish that.

Ellam said that Brown had told a meeting of his Cabinet on Tuesday that Britain could be prepared to intervene further to support the banking system.

But he declined to comment on specifics. “What we do not want to do is speculate irresponsibly about market-sensitive matters,” he said.

Like big investors, average British citizens would also benefit from a government-backed boost of confidence in the banking sector.

“I always thought RBS was a safe bank, and I had every confidence in it,” Henry Geller, a 55-year-old doctor outside an RBS branch in London on Tuesday morning said, speaking conspicuously in the past tense. “I'm a bit concerned.”

Both RBS and Barclays deny that they have sought money from the government.

Associated Press Writers David Stringer and Martin Benedyk in London contributed to this report.