More than £66bn of taxpayers' money invested in RBS and Lloyds TSB may never be recovered, MPs have warned.
The Commons Public Accounts Committee (PAC) , said that lessons needed to be learned from the sale of Northern Rock - and applied to decisions concerning any future sale of the banks "with value to the taxpayer taking precedence over speed of exit".
The MPs, who are charged with monitoring Government financial affairs, said that the Treasury made a series of costly mistakes in its handling of Northern Rock, which had to be taken into public ownership in 2008.
Just two bidders were interested in taking it over, sparking fears that the two remaining state-backed banks, RBS and Lloyds, will fail to be sold for a profit.
Auditors earlier this year estimated that losses on the Northern Rock rescue would amount to £2bn. That figure includes the loss of about £480m on the sale of Northern Rock Plc to Virgin Money, owned by Sir Richard Branson, last year.
The estimated losses were highlighted in a report in May by the National Audit Office (NAO) into the nationalisation of the bank in 2009 and its subsequent part sale.
The report criticised the then Chancellor Alistair Darling for failing to look at the full consequences to the taxpayer.
Labour MP Margaret Hodge, who chairs the PAC, said: "The lack of competition does not fill us with confidence that the taxpayer will make a profit on the sale of the two banks which remain in public ownership, RBS and Lloyds.
"There is a risk that the £66bn invested in RBS and Lloyds may never be recovered.
"It is vital that the final decisions on the wholly owned banks are made with value to the taxpayer taking precedence over speed of exit.
"This will not be the last banking crisis, and the next one is likely to be different. The Treasury must ensure it retains the right staff with the right skills to understand the risks and respond effectively.
"It needs to learn the lessons from the creation and sale of Northern Rock and make sure that these are applied in future, including to any sale of RBS and Lloyds."
The run on deposits at Northern Rock in September 2007 was an early and pivotal moment in the financial crash and subsequent meltdown.
After nationalisation, the bank was split into a mortgage lending and savings arm, Northern Rock plc, and Northern Rock (Asset Management) , which held its bad debt.
The move was supposed to generate lending but it fell well short of its £15bn target, reaching just £9.1bn.
The Treasury has accepted its part in a "monumental collective failure", according to the report.
It has now set up a dedicated team, UK Financial Investments (UKFI), to manage taxpayer shares in banks.
Earlier this year the Treasury's most senior official, Sir Nicholas Macpherson, admitted the taxpayer lost out because of five months of "drift" as the crisis unfolded.
A spokesman for the Treasury said the decision to nationalise Northern Rock in 2008 was taken in the interest of financial stability, and that the sale of Northern Rock plc to Virgin Money last year represented "good value for money for the taxpayer, and has helped increase high-street competition".
A Treasury aide added: "RBS and Lloyds have made good progress over the last two years and our goal remains the same: To get the best possible value for taxpayers."
Matthew Sinclair, chief executive of the TaxPayers' Alliance, said: "This report on the expected cost of the Northern Rock fiasco will come as a devastating blow for taxpayers who are already carrying a huge loss from the Government's stake in RBS."