By Daniel Hunter
UK accountancy giant Grant Thornton has been sued for £49 million by Manchester Building Society.
The Building Society has accused Grant Thornton of negligence over the auditing of its accounts between 2006 and 2013.
A spokesperson for Manchester Building Society said the accountancy firm gave poor and incorrect advice on how to account for interest rate swaps.
"The claim primarily covers Grant Thornton's advice and audit services relating to the implementation and application of hedge accounting by the society," said the building society.
As a result of the poor advice, the lender says it had to restate its 2011 results from a small profit to a £21.9m loss.
It then had to raise around £18m to cover the costs of the restated figures.
Grant Thornton has so far refused to comment.
It is also being investigated by the Financial Reporting Council (FRC), the body that investigates accountants. The probe started in April 2013 and is still ongoing.
"If the society is unable to reach satisfactory agreement with Grant Thornton the matter will progress to a court hearing," the society threatened.