MPs have urged the Financial Conduct Authority (FCA) to publish its full report into Royal Bank of Scotland's business restructuring division.
The report, which was leaked to the BBC last month, alleged the bank's troubled Global Restructuring Group (GRG) mistreated many of its clients, a claim the FTSE 100 giant has firmly denied.
GRG, which operated between 2005 and 2013, was introduced to help struggling business customers and it once handled approximately 16,000 firms. However, it has been accused of deliberately forcing businesses into difficult financial positions for its own benefits.
The investigation found 92% of "viable" firms seen by GRG experienced "inappropriate action", such as fees being imposed on them or interest charges being raised without notice. Only 10% of complaints made it back to RBS.
Treasury Committee chair Nicky Morgan has called for FCA chief executive Andrew Bailey to publish the report in full and without delay as the leak left the watchdog with "no control over the timing or content" of further public disclosures.
"The report is in the hands of an unknown number of third parties," she said. "The balance has tipped firmly in favour of full publication."
In November last year, Britain's financial regulator said a full report would be made public but so far it has not yet been published.
"The FCA told the committee in November 2016 that a 'full account' of the findings from the skilled persons' report would be published," Morgan said.
"Nearly a year later, and nearly four years since the report was commissioned, we are still waiting for answers. I have asked Mr Bailey to update the committee on any information that the FCA uncovers as part of its inquiry into the leak. This would not be the first instance of leaking from the FCA, but lessons must be learned to ensure it is the last."
The FCA replied saying it would "respond in due course" to Morgan's request, adding it had launched its own inquiry into the leak.
"We have already initiated a leak inquiry into the disclosure of the s166 report on RBS GRG to the BBC, and we have asked the other parties who had access to the report, namely RBS and Promontory, to do the same," it said.
"If the Treasury Select Committee or the BBC have evidence that the document was leaked by the FCA, we encourage them to share that with us."