Shares in some of Britain’s most popular mortgage lenders plunged yesterday amid fears that other banks would be hit by similar problems to Northern Rock.

Hundreds of customers again thronged to Northern Rock’s 76 branches to demand the return of their savings, while others inundated the bank’s website with requests to transfer their cash to other banks.

Customers have withdrawn more than £2 billion from the Newcastle-based bank since Thursday night, when it emerged that Northern Rock had applied to the Bank of England for an emergency loan to keep it in business.

The panic among Northern Rock customers forced Alistair Darling, the Chancellor, to promise yesterday that the Government would protect the estimated £28 billion in deposits still held by the bank. There were growing fears that banks with similar business models might also ask the Bank of England for a lifeline.

Alliance & Leicester (A&L) saw the value of its business slashed by a third yesterday, shares falling 273p to 600p each. Bradford & Bingley’s (B&B) share price slid 15 per cent to 279p each. In comparison, shares in high-street banks such as Royal Bank of Scotland fell by 4 per cent and Lloyds TSB by less than 2 per cent.

Like Northern Rock, A&L and B&B borrow from other financial institutions as well as using retail deposits to fund their mortgage lending. This way of doing business has been damaged by the collapse in the American sub-prime mortgage market, which made banks reluctant to lend to each other except at very high interest rates.

Banking analysts said that unless inter-bank lending went back to normal within a few months, A&L and B&B would suffer the same fate as Northern Rock. Northern Rock’s shares have more than halved in value since it went to the Bank.

Alex Potter, an analyst at Collins Stewart, said: “If the current irrational behaviour of the wholesale market doesn’t normalise by early next year, you’re looking at similar kinds of problems for these two banks.” The banks were also hit when analysts at Citigroup said that earnings at A&L and B&B would be lower than expected in the next two years. Citigroup said that B&B would be particularly badly affected if rising interest rates meant that more people defaulted on their mortgages, because it had a high proportion of customers who self-certified their wages when applying for a loan.

But financial advisers said it was too early to panic about Northern Rock’s rivals. Brian Dennehy, of Dennehy Weller & Co, the independent financial adviser, said: “Alliance & Leicester has borrowed more from the markets than many other lenders, but it is still nothing near as much as Northern Rock. Borrowers and savers should not panic, there is nothing to suggest that their money isn’t safe.”

Mortgage brokers warned customers that they may face a penalty charge if they moved their Northern Rock mortgage to another lender. James Cotton, of London & Country, said: “Most borrowers are locked into specific deals which the lender is duty-bound to honour. Borrowers who pull out of a home-loan deal early could be forced to pay high penalty fees, which is another reason to stay put.”

An A&L spokeswoman insisted that the bank had no intention of applying to the Bank of England for an emergency loan. A&L, which has a 4.2 per cent share of the mortgage market, recently reported a strong set of interim results, with half-year profits up 10 per cent to £295 million.

Northern Rock hopes that its temporary, unlimited line of credit from the Bank will allow it to keep selling mortgages while finding a buyer for the business. Lloyds TSB cast an eye over Northern Rock more than a week ago but was put off by uncertainty in the global credit markets, as well as the fact that the Bank of England loan would not have come with Northern Rock if it was taken over.

Northern Rock said it was not in talks with bidders, but that its board was “actively considering all strategic options”. It reiterated that the Government had guaranteed the safety of its accounts. “The Chancellor’s statement makes it clear beyond any doubt that all savings in Northern Rock are safe and secure,” the bank said.

Previous reassurances have, however, failed to deter customers from withdrawing their savings. The bank’s branch in Moorgate, in the City of London, said that it was able to see 20 customers an hour and would stay open for an additional hour until 6pm but by 4pm a queue of about 60 customers, mostly pensioners, was still waiting.

At the Houndsditch branch in east London, George Payan, 72, queued to withdraw £83,000. He said: “When you have large savings in an account that is unreliable, you want to get it out.”

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