Royal Bank of Scotland has denied allegations that it mistreated small business customers Reuters

The Financial Conduct Authority's (FCA) refusal to publish a report into allegations that Royal Bank of Scotland (RBS) mistreated small business customers has been criticised.

FCA chief executive Andrew Bailey told MPs on the Treasury Select Committee that publishing the report could reveal confidential information and that he did not believe public interest was best served by making it public.

The 2014 report concerned allegations that RBS mistreated 12,000 small business customers through its now-defunct Global Restructuring Group (GRG).

A copy of the full report was leaked to the BBC in August, revealing that struggling businesses were weighed down with debt and fees and only had a slim chance of returning to the main bank from GRG. RBS, however, has denied allegations that it mistreated customers.

Bailey said he recognised that public interest justified greater disclosure of material in the report and that the FCA would release a "detailed summary" of the findings after it is vetted by external lawyers.

But a spokesman for the RBS-GRG business action group, which represents more than 500 businesses, criticised the FCA's refusal to publish the full report as "shocking and unconscionable".

"Tens of thousands of people whose jobs, businesses or livelihoods were destroyed by RBS desperately want this report published," he said.

"Our elected MPs want this report published. The only person who doesn't want this report published, it seems, is Andrew Bailey.

"We have no confidence in the FCA's promise to publish a summary of the report. It already published a summary in November 2016 which we now know was woefully inadequate."

Conservative MP Nicky Morgan, who chairs the Treasury Select Committee, said there was an "overwhelming" case for the report to be made public.

"The report is now in the hands of an unknown number of third parties," Morgan said in a statement.

"If closure is ever to be brought to this long-running issue, parliament and the public need the account ordered by the regulator.

"Those affected have a right to know what really happened."