GORDON BROWN'S gamble on Northern Rock appeared to have paid off last night as the troubled bank's shares rebounded and calm returned to the stock market.

The Prime Minister put his personal credibility on the line when he authorised the Chancellor's pledge to guarantee deposits at the bank, which was under siege from savers trying to get their money out.

But the Government's guarantee appeared to have done the trick last night as the queues outside Northern Rock branches disappeared and savers accessing online accounts fell by half.

The Government intervention buoyed banking sector shares across the board, with lenders such as Alliance and Leicester clawing back some of the value they lost on Monday.

Experts warned last night that the next few days would be critical for Northern Rock's future. They said the bank was still likely to be bought out.

But there were faint signs of hope as loyal savers rallied to the bank's cause - particularly in the North-East.

Eighty per cent of phone callers were asking how they could reinvest their money, according to the bank - although the amount of cash flowing back into Northern Rock is nowhere near the £3bn taken out.

The bank even offered customers an incentive to return.

A spokesman said: "Any

customer who had to pay a charge or transfer fee to withdraw money due to concerns about the current situation will have that money refunded - if they reinvest those funds in the same kind of account with us by October 5."

By 10am yesterday, there were queues at only four branches in the bank's network of 76.

Calls to the bank's call centre fell by more than 90 per cent and half as many customers were accessing their online accounts.

But online customers faced a new threat last night.

Credit reference agency Equifax said fraudsters had been trying to exploit the uncertainty surrounding the group with a swathe of email frauds.

Bogus emails sent to Northern Rock customers asked them to click on an internet link and enter details about their account and their password.

Neil Munroe, external affairs director at Equifax, said: "Fraudsters think nothing of taking advantage of a bad situation for their own gain."

On the markets, banking stocks recovered as the Bank of England announced a £4.4bn cash injection to ease the pressure on lending rates between banks.

Northern Rock shares were also up more than eight per cent on the day, although they have still not recovered from the losses of Friday and Monday.

In his first public comments since the crisis broke last week, the Prime Minister said: "Everything that can be done will be done and is being done to maintain the stability of the economy.

"We are an economy that will continue to grow, continue to create jobs, continue to have low inflation.

"Everything that has been put in place in the past two days is designed to ensure that."

Chancellor Alistair Darling confirmed similar support would be offered to any other bank hit by the turmoil caused by the collapse of the sub-prime mortgage lending market in the US.

Earlier, the Financial Services Authority (FSA) said it was looking at ways of strengthening the system of compensation for depositors in order to prevent any repeat of the loss of confidence that hit Northern Rock.

FSA chief executive Hector Sants said it would be reviewing the existing industry-backed compensation system, which only protects the first £35,000 of depositors' savings in the event of a bank collapse.

He said many of those who had been queueing to withdraw their savings from Northern Rock had considerably more deposited with the bank.

Although the Government has provided some respite for Northern Rock, most analysts still expect it to be sold.

Credit Suisse estimates Northern Rock is still worth between 340p and 390p a share. Yesterday, it closed up at 306p.