Gordon Brown has been forced to defend claims that taxpayers will only get "rubbish" parts of Northern Rock.

Critics say the bank's prime assets will remain in a private "financing vehicle", leaving the public exposed to an unacceptable risk.

Concerns were raised as parliament debated legislation which would allow ministers to take the bank into "temporary public ownership".

The Banking (Special Provisions) Bill details how the Government will buy the mortgage lender's shares at a level to be defined by an independent figure.

But for technical reasons Northern Rock uses a separate firm called Granite to buy the best mortgages and resell the debt.

The treasury would not own this entity under the arrangements.

Shadow chancellor George Osborne said this would mean the taxpayer would "come last".

He said: "Now everyone knows that the way Northern Rock and Granite will operate under nationalisation leaves the taxpayers saddled with all the bad debts, with Granite taking the best mortgages."

And Lib Dem leader Nick Clegg told Mr Brown during Prime Minister's Questions: "You now seem to be jeopardising the interests of British taxpayers all over again by hiving off the bank's best assets elsewhere."

But Mr Brown responded that the arrangement would not prevent the Treasury from recouping its investment.

He said: "As far as Granite is concerned, I can assure you that will not affect the sale of Northern Rock to a private buyer."

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