The FRC has also launched an investigation in connection with Grant Thornton UK LLP and Manchester Building Society into the accounting and auditing of interest rate swap arrangements which 'gave rise to a prior period adjustment in the financial statements for the year ended 31 December 2012'.

The FRC said it launched the probe after receiving information from the Prudential Regulation Authority in relation to the conduct of the then auditors, Grant Thornton UK.

The latest investigation is the FRC's second into GT in as many days. It follows hot on the heels of the probe announced yesterday (6 August 2013) into whether Grant Thornton, auditors to soft drinks group, Nichols plc, was independent at the time of conducting the audits of the company's financial statements for the years ended 31 December 2011 and 2012.

In 2011, the total audit fee for the parent and group by parent company was £67m, of which £62m was attributed to the building society.

A Grant Thornton spokesman said: 'We acknowledge the FRC's statement regarding their investigation. The FRC and Grant Thornton have a common interest in promoting good corporate governance and reporting standards and as such we alerted the regulator as soon as we became aware of a potential issue. We shall, of course, fully cooperate with any investigation. As a firm, we continue to strive to deliver quality work for our clients.'

Chris Gee, MBS finance director, said: 'The society will provide the FRC with any assistance that it can in its enquiries.'