Fears about the future of Northern Rock grew on Friday as shares in the Newcastle-based lender slumped and customers lined up to withdraw funds.

The mortgage lender said in a statement on Friday that the Bank of England had agreed to provide it with as much funding “as may be necessary” as it warned that it would otherwise be incapable of refinancing maturing liabilities and flagged that full-year profits would be 20 per cent below consensus forecasts.