Worried savers have continued to flock to Northern Rock bank branches to withdraw their savings, following similar scenes over the weekend.
Bank boss Adam Applegarth said people could withdraw money and that it was "business as usual", while Chancellor Alistair Darling appealed for calm.
About £2bn has been withdrawn since Thursday, when the bank applied to the Bank of England for emergency funds.
In Monday morning trading, shares in Northern Rock were down by 33%.
Shares in fellow mortgage banks also suffered.
In morning trade in London Northern Rock's shares, which had lost 32% on Friday, fell from 438 pence to 293 pence. Shares in mortgage lenders Alliance & Leicester and Bradford & Bingley were also down, by 14% and 11%.