Goldman Sachs is close to putting together a £15bn funding package which might allow one of the groupings eyeing Northern Rock to proceed with a bid for the stricken mortgage lender, according to a weekend report.

The Sunday Times reported that the US investment bank had lined up debt to fund a deal on better terms than packages being negotiated by rivals including Citigroup, in a development that could break the logjam affecting the sale.

Britain's highest-profile casualty of the credit crunch is in talks with at least two suitors - investment group Olivant and preferred bidder Virgin - and advisers are confident a deal to rescue the bank can be salvaged in January.

However, while the government is anxious that Northern Rock should be rescued by a private sector bidder, the prospect of a sale seemed to become increasingly remote in the weeks before Christmas.

Amid reports that some banks were shying away from providing loans to fund a takeover of Northern Rock, financing worries have loomed over the deal.

Fears of a downturn in the UK housing market have made it increasingly hard to value the bank and its assets, prompting some potential suitors to withdraw and increasing the threat that the bank may have to be nationalised.

However, speaking on BBC television, Prime Minister Gordon Brown said yesterday: "We don't rule out any options but the preferable options, as we know, are the private sector bids that are in play at the moment. They are being looked at very carefully."

Brown said Goldman Sachs, which is advising the government, would report "very soon".

Northern Rock is estimated to have borrowed just over £26bn from the Bank of England since mid-September after struggling to raise funds in wholesale markets.

Brown, who has come under fire for his handling of the Northern Rock crisis, said the government had avoided contagion throughout the rest of the economy "so far" and that taxpayers' money was secure.

Northern Rock declined to comment. Goldman Sachs was not immediately available for comment.

The sale process could be complicated further next week when shareholders will vote on a resolution which gives them the right to vote on whether assets can be sold or new shares issued.

Hedge fund RAB, which has 7.7% of Northern Rock shares and is a top investor alongside 10% owner SRM, has written to investors urging them to back the EGM resolutions.