In the weeks since the chaos began to unfold around the floundering lender, it had borrowed an estimated £20.6 billion at New Star economist Simon Ward's last count - a figure which the BBC is reporting has now risen again to reach almost £23 billion.
According to the BBC, this equates to roughly £730 for each UK taxpayer.
BBC business editor Robert Peston said: "We are talking about total public-sector exposure to the Rock of £40bn - equivalent to around 3 per cent of our entire economy. And that exposure could become much bigger, as other loans to the Rock fall due for repayment. "
Later on Thursday, Mr Peston learned that Northern Rock and the Bank of England were projecting that the firm would have borrowed "a staggering £30bn from the Bank of England" by year end, he said.
