Virgin Group's takeover offer for Northern Rock is too low, a key shareholder in the troubled lender said tonight.
The development comes after Northern Rock named Sir Richard Branson's Virgin as its preferred bidder, two months after turning to the Bank of England for an emergency loan.
But investment management firm RAB Capital says that Virgin's offer, which includes the immediate repayment of £11 billion of the £25 billion borrowed from taxpayers and values Northern Rock at about £200 million, does not represent good value for shareholders.
"We welcome today's developments as they are a step closer to securing the inherent long term value in the business for current shareholders," said RAB Capital chief executive officer Philip Richards.
"However, we do not believe that this proposal reflects the true value of Northern Rock and we would expect either that this proposal be improved or that alternative proposals be brought forward which would combine a similar repayment schedule for the Treasury together with improved terms for shareholders."
If Northern Rock investors were to block a sale, the company would likely either be put into administration or nationalised.
Speaking at the Confederation of British Industry (CBI) today, Gordon Brown defended the government's handling of the banking crisis.
The Liberal Democrats are among those calling on the government to nationalise the bank.
Mr Brown told business leaders today: "We have taken difficult decisions to steer a course of stability and protect the taxpayer which have led to today's announcement by the company of a preferred bidder."
Under the terms of the deal, Virgin Group would also invest £1.3 billion in the bank, half of which would be funded by sales of new shares.
The takeover bid would see the consortium hold a 55 per cent stake in the bank, leading shareholders with 45 per cent.
Bryan Sanderson, chairman of Northern Rock, said today: "This is very good news for Northern Rock. Over the last few weeks and months we have looked at these issues from the perspectives of all stakeholders."
Despite a potential solution to Northern Rock's woes, the government has faced continued criticism over its economic competence.
Also speaking at the CBI conference, Lib Dem acting leader Vince Cable claimed Mr Brown and Alistair Darling have risked economic stability with a series of poor business decisions.
In his own keynote speech this morning, Mr Brown defended his government's economic record.
He accepted the past 12 months had been challenging, "most recently in the form of financial turbulence and credit problems whose origins are clearly international but whose full implications are still unfolding".
Mr Brown said he had made the "difficult decision" to bear down on rising inflation by staging public sector pay - which placed the former chancellor at uncomfortable odds with the unions.
The prime minister said the government would take "no risks" in the future.
He told business leaders: "There will be no irresponsible relaxation of pay discipline, no unfunded spending commitments, no unaffordable promises and no short-term giveaways."
Despite the prime minister's tone, the Brown-Darling team faces another uncomfortable week.
The Conservatives are calling on Mr Darling to make another emergency statement before MPs today, amid mounting evidence of routine procedural breaches at HM Revenue and Customs (HMRC).
Shadow chancellor George Osborne said: "Alistair Darling's claim that the catastrophic loss of people's personal data was down to one junior official is now so discredited that it's hard to imagine anyone believes it.
"So many other examples of a systemic failure to protect data at HM Revenue and Customs have been brought to light that the chancellor must make an emergency statement to the House of Commons tomorrow afternoon explaining themselves."