The government, which has final say on a solution, has made it clear that nationalisation remains an option if private buyers fail to raise enough funds to immediately repay the more than $49.3bn that Northern Rock has borrowed in emergency loans from the Bank of England.
The move came as Northern Rock shareholders failed to stop the bank's board from finding a private buyer as it tried to reach a rescue deal.
The bank's stakeholders, hedge funds SRM Global and RAB Capital, sought to restrict a possible sale, fearing that the board might succumb to political pressures, but fell short of the necessary votes.
A government takeover of Northern Rock means shareholders could be left with very little, or nothing, of their investment.
Alistair Darling, the finance minister, said on Tuesday that a private sale was the preferred option but did not rule out nationalisation.