LONDON (Bloomberg) - Northern Rock plc., which suffered the first run by UK bank depositors in more than a century, may remain nationalised for years to come, according to the chairman appointed by Prime Minister Gordon Brown's government.

"We are clearly talking about a period of some years," Ron Sandler, who was appointed by the Treasury to lead the bank, said at a press conference yesterday in Newcastle, England.

Mr. Brown said he wanted a "temporary period" of ownership for the bank that tapped UK authorities for loans and guarantees of £55 billion ($107 billion) since September, when its credit lines in financial markets dried up.

Bringing the bank under the wing of the state will leave Government ministers responsible for assets of £113 billion and 6,500 employees, damaging Mr. Brown's reputation for smooth management of the economy. The Conservative opposition said it would vote against the matter when it comes before Parliament.

"Let's be in no doubt about what a disaster this day is," said David Cameron, leader of opposition Conservative Party. "The nationalisation of Northern Rock is a disaster for the British taxpayer, a disaster for this Government and a disaster for our country."

Mr. Sandler, who advised the government on pensions and brought back Lloyd's of London from the edge of bankruptcy in the late 1990s, will earn £90,000 a month acting for the government as Northern Rock's executive chairman. Former Swiss Re Group executive Ann Godbehere will become finance director, earning £75,000 a month.

"This bank will not write as many mortgages as it has done," Mr. Sandler said. He declined to discuss how many jobs his team would eliminate or when it would make decisions.

The move to acquire Northern Rock is the biggest bank nationalisation since Clement Attlee's Labour government brought the Bank of England into public control in 1946.

The government last acquired a bank in 1984 under Conservative Prime Minister Margaret Thatcher. Then, the Bank of England purchased Johnson Matthey plc.'s lending operation for £1 to support assets of £400 million. The gold refiner had expanded its commercial loans business and racked up bad debts. A decade before, the government rescued Slater Walker Securities by advancing about £70 million.

The British government last nationalised a major company in October 2002, when it acquired Railtrack, owner of the nation's railroad track and stations.

"It is quite a historic step to have taken," Angela Knight, chief executive of the British Bankers' Association, said in an interview on Bloomberg Television. "It has hung like a cloud over the UK banking system."

Chancellor of the Exchequer Alistair Darling introduced legislation into Parliament that would enable the government to take control of any failing bank. The House of Commons will debate and vote on the bill today.

"There is a perception that Darling is not up to the job and that he has made the wrong judgments through this whole episode," said John Curtice, author of "The Rise of New Labour" and a professor of politics at Strathclyde University in Glasgow. "This has been far more than a drip. There is no doubt that this will damage their reputation."

Mr. Darling said the government would need to keep control of the bank until financial markets recover from the collapse of the sub-prime mortgage market in the US last year. Mr. Brown, at a press conference in London, refused to guess how long nationalisation would last.

"We want to get the bank back into private ownership after a temporary period of time," Mr. Brown said. "That will depend on how the markets recover."

Standard & Poor's raised its rating on Northern Rock debt to A from A- after the government decision to nationalise the bank. The rating applied to long-term debt owed by the bank.

Mr. Darling and Mr. Brown defended their efforts to rescue the bank, saying failing to act when customers lined up to withdraw deposits in September would have put the rest of the UK financial system at risk.

"There were choices to be made," Mr. Darling said. "We could have let the bank go under. But the risks to the wider financial system, for savers and the general public were not acceptable."

Mr. Darling's proposed legislation will give the government sweeping powers to seize any other bank that runs into trouble. That authority, the Treasury said, would expire in a year and will be used only to preserve the stability of the financial system or the interests of taxpayers.

The government aims to bring the measures into law within days with the support of the Liberal Democrats, the third-biggest UK political party.

"The government has taken far too long, but they are now in the right place," Vince Cable of the Liberal Democrats, who speaks on finance, said in a Bloomberg Television interview. "This bank will have to be downsized. It will be painful for people in the northeast."

The Conservative opposition, pointing out Labour's historic support for state control of the economy, plans to vote against the rules. Labour governments in the 1970s under Harold Wilson and James Callaghan nationalised ship and aircraft builders and British Leyland Motor Corp.

After the Bank of England provided emergency funds in September, Mr. Darling sought bids to take over Northern Rock and considered detailed plans from the company's own managers and Richard Branson's Virgin Group Ltd. Both offers needed more than £1 billion in subsidy from the Treasury.

"All of us in the Virgin consortium are very disappointed that the government has chosen to opt for nationalization," Mr. Branson said in an e-mailed statement. "However, we must accept the decision with good grace and hope that the Rock will somehow find better fortune in the future."