Northern Rock has further increased the scale of its borrowing from the Bank of England, suggesting, according to one commentator, there has been a larger withdrawal by retail investors than previously thought.

The Newcastle-based lender borrowed a further £4.7bn ($9.5bn) from the Bank last week, it emerged on Thursday, taking the total to about £21bn. Six weeks after Northern Rock first went to the Bank for support as lender of last resort, its weekly borrowing has climbed from £3bn in the week to October 17 and £2.3bn the week before. The figures were revealed in the weekly publication of the central bank’s balance sheet.

Simon Ward of New Star, the fund manager, said: “The scale of the loan and its continued rapid increase suggest that, as well as losing wholesale funding, Northern Rock has suffered a larger withdrawal by retail customers than the guesses of several billion pounds circulating in the market.”

Alistair Darling said on Thursday he expected Northern Rock’s directors to come up with proposals by February to end the bank’s reliance on government support. Stressing this was not a “drop dead” date, Mr Darling said, nonetheless, he hoped Bryan Sanderson, who became Northern Rock chairman after Matt Ridley’s decision last week to resign, would come up with such a plan.

“Northern Rock needs to play its part too now and I hope the new chairman will put new vigour into sorting things out,” he told MPs. “I really want to get to get across to the bank that they have got a breathing space. They have got to consider their options.”

Mr Darling criticised Northern Rock’s management for failing to have a “fallback position”, such as standby creditlines, given its dependence on wholesale markets for funding. This had left it exposed when liquidity dried up in August, forcing it eventually to turn to the Bank of England.

He said the bank could have managed better the queues that outside its branches during last month’s bank run, which only ended when the government promised to guarantee depositors’ savings.

Mr Darling also criticised the Financial Services Authority over its scrutiny of Northern Rock’s business model: “In hindsight, it would have been much better if the FSA, when first looking at Northern Rock, had said: ‘Hold on, what is your fallback position?’”

He rejected assertions that the run could have been avoided had the Bank of England intervened to provide liquidity earlier.