TAXPAYERS will be left with a £2bn bill from the collapse and rescue of Northern Rock, parliament’s spending watchdog will warn today.

The sum is the amount that will never be recovered from the £37bn pumped in by the Treasury when the Gosforthbased lender went bust in 2007, the National Audit Office (NAO) said.

The verdict is an embarrassment for the Treasury, after a report in February, suggested taxpayers would enjoy a £11bn bonanza from the Rock’s period of public ownership.

That conclusion was reached by UK Financial Investments, the body that controls the state’s stakes in bailed-out banks on behalf of the Government.

However, last night a senior MP said taxpayers were fortunate that the £2bn bill was not even higher “given the scale of the crisis” that engulfed the banking sector and the economy.

And, crucially, the NAO backed the controversial £747m early sale of Northern Rock to Virgin Money as the best deal to protect the taxpayer from further losses.

Labour had protested the Rock’s buyers could raid its cash reserves after the purchase, to reimburse themselves and, effectively, buy the bank for nothing.

In November, it was revealed that £250m of Northern Rock’s own money was being used to part-finance the sale, prompting accusations of asset-stripping.

But today the watchdog concludes that – while the deal will lose the taxpayer £480m – that money will be recovered from the likely rising value of Northern Rock assets remaining in public ownership.

And it sharply criticises Labour’s handling of the saga when, in 2009, the Treasury split the Rock in two without “looking in detail at the possible consequences for the taxpayer”.

While the decision was “reasonable”, it was based on an “optimistic” business plan prepared by Northern Rock management and lending fell short of targets.

The report may be the final verdict on the spectacular collapse of the bank – which has 75 branches, one million customers and holds £14bn of mortgages – given that the sale to Virgin Money went through at the end of last year.

It bought Northern Rock plc – the so-called “good bank”, funded by retail deposits – which was split off from Northern Rock (Asset Management), the “bad bank”, which retains troubled loans in the public sector.

It is the “bad bank” that is now expected to leave taxpayers with a £2bn loss, although those assets and liabilities will not be fully wound down.

Margaret Hodge, Labour chairwoman of the Public Accounts Committee, said: “Based on this report, it seems the decision to go ahead with an early sale was the right one.”

She added: “Given the scale of the crisis, we are fortunate that the net present cost to the taxpayer is potentially not more than £2bn. But this is, perhaps, more by luck than good judgement.”