The accountancy watchdog has drafted in a top City law firm to probe the leak of an impending judgement against PricewaterhouseCoopers, the world's biggest auditor.
Sky News has learnt that the Financial Reporting Council (FRC) has asked Reed Smith to investigate the premature disclosure to a national newspaper of a tribunal verdict resulting in a £6m fine for PwC.
The appointment of an external legal advisor is aimed at ensuring the independence of the inquiry, according to one insider.
It follows an email from Stephen Wooler, an FRC member and barrister, to a journalist at The Times, which highlighted the newsworthiness of a forthcoming ruling on PwC's auditing of Connaught, a collapsed social housing maintenance provider.
In the email - parts of which have been reported previously, and which has been seen by Sky News - Mr Wooler related a discussion he had had with Gareth Rees QC, the FRC's executive counsel, about a candidate for coverage in the newspaper's legal section.
There is no suggestion that Mr Rees was aware of Mr Wooler's intention to prematurely leak the outcome of the tribunal to a journalist.
Mr Wooler wrote that the FRC was "keen to raise awareness of the work it does in relation to professional discipline as regards accountants and actuaries", describing it as "high profile and fascinating".
He referred to ongoing cases being investigated by the watchdog, including Tesco (Frankfurt: 852647 - news) 's profit overstatement, BHS and "the client accounts of Barclays Bank (NYSE: BCS-PA - news) ".
The leak probe comes at a particularly inopportune time for the FRC, which is being lined up to acquire substantial additional powers and responsibilities in the areas of corporate governance and executive pay.
In a report published on Wednesday, the Business, Energy and Industrial Strategy Select Committee urged the Government to hand the FRC a wider range of duties, funded through a new levy.
One insider said Mr Wooler's remark in his email that the FRC's findings against PwC could not match "the public opprobrium that the firm attracted over the Oscars fiasco" was significant.
Regulators in sectors such as banking, telecoms and energy have come under pressure since the financial crisis to demonstrate that they are discharging their disciplinary functions with sufficient vigour.
The FRC said: "We take breaches of confidentiality seriously and will investigate the matter fully."
A PwC spokesman said: "We are concerned by the breach of confidentiality and welcome the Tribunal's request for an investigation.
"We are confident that the FRC will conduct a thorough investigation and wait to hear the outcome."