Thousands of Northern Rock shareholders, many of whom have owned the stock since it converted from a building society more than a decade ago, have been urged to “prepare for the worst” and expect to get nothing back from their investment.

Northern Rock’s shares were suspended at 90p today following chancellor Alistair Darling’s decision to take it into public hands at the weekend. It was the first nationalisation of a bank in modern times.

The bank’s 100,000 or so small shareholders are now unable to trade their stock and face an agonising wait to find out it their investment has any value.

Darling said that he would appoint an independent arbitration panel to value the bank and calculate any compensation due. However, this process will take months and will assume the bank never received government help – meaning the shares could be deemed to be worthless.

Even in a best case scenario, analysts said today they could be worth as little as 5p a share. This compares with a high of £12.51 on February 9 2007 - 93 per cent higher than today’s suspension price.

The shares are down 86 per cent since September 13, when it was first revealed that the bank had sought emergency funding from the Bank of England.

Even longer-term shareholders are sitting on heavy losses – the shares are down 81 per cent from the 470p at which they floated in October 1997.

Here we answer your questions.

I am a shareholder. What can I do?

Unfortunately, very little. You can not trade your shares since their suspension this morning, and you must wait several months for an independent panel to work out what your shares are worth.

The panel will have to work out what the shares are worth without the benefit of billions of pounds of government help. Without this, the bank may well have gone into administration anyway, prompting many analysts to speculate that the shares are effectively worthless.

However, others pointed out that the bank still owns valuable assets, not least its branch network, so shareholders could still get something – albeit they should not bank on much.

Richard Hunter of stockbroker Hargreaves Lansdown said: “I would expect the worst and then anything else will be a bonus.”

There is one glimmer of hope in that several large institutional shareholders, such as hedge funds SRM and RAB Capital, have pledged to sue the government, arguing that the firm’s net asset value is 400p a share.

I have my mortgage with the bank. What happens now?

You must continue to make your monthly remortgage payments. The bigger question is what to do when you reach the end of your two-year fixed or tracker rate.

Mortgage brokers say that the bank has effectively priced itself out of the market, offering deals that are as much as one percentage point higher than the competition, so you should certainly look elsewhere.

And my savings?

The government continues to guarantee savings with Northern Rock under a deal put in place in September. This stated that all accounts that existed at midnight on September 19, including new deposits made into them, would be guaranteed.

All new retail deposits made after that date also benefited from the guarantee.

Northern Rock is offering some great rates. Is it worth taking one out?

The bank is offering a best-buy one-year fixed rate at 6.45 per cent. While this is not at the very top of the tables – West Bromwich takes the top spot with a rate of 6.75 per cent - it is the only one where your savings are fully guaranteed by the government. At other banks, compensation is limited to £35,000.

However, such good rates are unlikely to last for long, as Northern Rock will not be able to seek customers under the nationalisation plan.

Kevin Mountford of comparison site Moneysupermarket said: “It’s certainly where I would be putting my money. It’s a no brainer really – especially as we don’t know how long these rates will last.”

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