The boss of Northern Rock last night made a direct appeal to customers of the embattled mortgage lender, calling on savers to stay the course. But he promised that anybody who wanted their money back could have it.

Adam Applegarth, the bank’s chief executive, sought to reassure customers in a message on its website. “Your savings are secure and there is no need for you to withdraw your money based on our recent announcement,” he said, amid fears that the bank faces a second wave of withdrawals from panicking customers.

Branches up and down the country were besieged on Friday and Saturday, after news of the Bank of England’s bail-out was disclosed. About £2 billion is believed to have been withdrawn in savings since the beginning of business on Friday morning.

However, about 15 per cent of savers have deposited money with the Newcastle upon Tyne-based mortgage lender through postal accounts, which are believed to hold as much as £10 billion on deposit. And 11 per cent of its savers hold accounts that limit short notice withdrawals.

This weekend the Financial Services Authority reiterated that Northern Rock was fit for business. Sir Callum McCarthy, its chairman, said: “If we believed that Northern Rock was not solvent, we would not have allowed it to remain open for business.”

Meanwhile, the crisis triggered a political row as David Cameron accused Gordon Brown of failing to rein in a decade-long credit boom and of basing Labour’s own economic policies on the same principle. His intervention triggered nervousness and anger in the Treasury and Downing Street. Labour sources accused Mr Cameron of “stirring it up for political gain”. One adviser said: “At a time when all of us ought to be reassuring people – after all, the FSA’s judgment is that this bank is sound – Mr Cameron’s behaviour is grossly irresponsible.”

Mr Cameron criticised Mr Brown and the Chancellor for their “virtual silence” over the past decade as Britons’ personal debt trebled to £1.3 trillion. He proposed new controls and checks on lending, such as allowing lenders to swap details of people with a poor credit history and a ban on banks raising customers’ credit limits without consent. Mr Cameron also widened his attack to Mr Brown’s handling of public finances, arguing that Government borrowing of £35 billion a year was a risk to stability. “Under Labour our economic growth has been built on a mountain of debt. And as any family with debts knows, higher debt makes us more vulnerable to the unexpected,” he wrote in The Sunday Telegraph.

Alistair Darling, the Chancellor, toured TV and radio stations claiming that Mr Cameron had got it wrong. He said that the Conservative leader had failed to understand the causes of a global problem and insisted that Britain’s economy was sound.

Mr Darling told The Times: “For him [Mr Cameron] to claim that this is all the fault of one of the strongest economies in the world is a nonsense.”

The Bank of England also faces criticism of its role, after the announcement that it had agreed to offer an emergency borrowing facility to Northern Rock triggered the withdrawal rush. Mervyn King, the Governor, will be grilled by the Commons Treasury Committee on Thursday.

Private investors who hold Northern Rock shares are steeling themselves for more misery with the share price expected to slide further today. It dropped by more than 30 per cent on Friday, having already fallen by 40 per cent since June.

Brian Dennehy, of Dennehy Weller, an independent financial adviser, said: “Northern Rock shareholders are going to be the ones who take the pain.” Some 800,000 savers and borrowers received 500 shares worth 452p each when Northern Rock demutualised ten years ago. But private investors had been piling in, keen for a slice of the action that helped boost the shares to a high of £12.50 in February.

Some experts are recommending those who still have shares to get rid of them as quickly as possible. Mr Dennehy said: “Private investors should follow the lead of fund managers.”

But Philippa Gee, of Torquil Clark, another adviser, said that investors should make a decision once they see the price. “The shares have already taken a battering and for most people the damage will already be done.”

Is it safe to leave money in a Northern Rock Account?

The Bank of England is providing funds to Northern Rock because it has cash-flow problems. It says that it believes that the bank’s business is solvent and that it can continue to trade.

If it’s solvent, why is it in trouble?

Northern Rock built its mortgage business very quickly by borrowing money from other banks. These have become reluctant to lend to each other due to the crisis over unsafe lending to American homeowners. Although Northern Rock had no significant business in America, interbank lending has virtually dried up, leaving it short of cash.

Will Northern Rock be sold?

The bank’s adviser, Merrill Lynch, has tried to arrange a rescue over the past month and is believed to have talked to Lloyds TSB and Royal Bank of Scotland. The chief City watchdog, and the Bank of England are all keen for a rival bank to bail out Northern Rock.

If it is solvent, why has no bank offered to take it over yet?

A buyer would need to refinance Northern Rock’s business. Due to the state of the lending market, potential acquirors want support from the Bank of England. The Bank was reluctant to allow a new owner to continue to benefit from its emergency loan facility. However, it is now considering allowing the emergency funding to continue for a period following a takeover.

Can the Government step in?

The Treasury might be restricted from providing guarantees under European law, which prohibits state aid to the private sector.

Where are my savings safe?

Savers are advised to spread their money among different banks to spread risk. National Savings & Investments is backed by the Treasury and deposits are “100 per cent secure”.

What if a bank goes bust?

The Financial Services Compensation Scheme guarantees to repay the first £2,000 of your savings and 90 per cent of the next £33,000. The maximum guaranteed amount you will receive is £31,700.

Are any other banks in difficulty?

No one can be certain, but Northern Rock’s business model was unusually aggressive. Leading high street banks have large branch networks and a strong base of depositors. They do not rely as heavily on interbank markets to fund their lending.

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