LONDON - The search for a private buyer for Northern Rock could go on for several more weeks, Prime Minister Gordon Brown said on Wednesday, but he left open the option the stricken lender could be nationalised.

"In the next few weeks we are looking at the situation of how we can find buyers for Northern Rock and I think everyone (in parliament) would say that we should rule out no option in doing so," Brown told parliament.

Shares in Northern Rock crashed over 20 percent to a record low earlier on Wednesday as expectations mounted that the bank will be brought under state control.

Brown fuelled that speculation on Tuesday by going into more detail than he has done previously about what would happen if the bank was nationalised.

"Because stability is the issue, we will look at every option and that includes taking the company into public ownership and then moving it later back into the private sector," he said in an interview with ITV news.

Northern Rock has borrowed about 26 billion pounds from the Bank of England after being hit by the global credit crunch, when it became the first British bank in more than a century to suffer a run of customers withdrawing their deposits.

Political commentators say Brown is reluctant to countenance nationalisation, partly because of its associations with the more left-wing Labour governments of the 1970s when Britain was in steep economic decline.

The Labour Party lags the Conservatives in the opinion polls, hit by a series of government blunders, the Northern Rock crisis and the worsening economic outlook.

NEED FOR STABILITY

Brown defended his handling of the Northern Rock crisis on Wednesday as the opposition accused him of dithering and delaying in finding a solution.

"We had to intervene to ensure stability, so the instability of Northern Rock would not spread out across the economy. That is what we've achieved over the last four months and the opposition should be supporting us not criticising us," he said.

Brown said it was still the government's intention that all the taxpayer support for Northern Rock would be repaid, but he refused to answer questions about how much public money had been committed.

Brown refused to confirm the figure when asked by Conservative leader David Cameron if total taxpayer support for Northern Rock, including guarantees, was now 55 billion pounds, saying he would "not provide a running commentary on figures".

Cameron accused Brown of indecision when he could have pushed for a quick sale to Lloyds TSB soon after the crisis broke out.

Brown said his advisers had not counselled him to push for an immediate sale after the bank run and said there had been no offer from Lloyds TSB.

Industry sources have previously said Lloyds TSB came closest to buying Northern Rock and held talks but did not make an offer.

Northern Rock shareholders on Tuesday backed proposals to curb some of the board's powers but stopped short of forcing it to ask for approval for any asset sales.

Bryan Sanderson, Northern Rock's chairman, said he was "reasonably confident" the bank could avoid nationalisation and talks with two suitors continue, while a standalone solution was still possible.

But he said financing a rescue package remained a challenge and a decision on nationalisation rested with the government and not the board.