More than a 1,000 companies have made accusations about practices carried on at RBS's Global Restructuring Group (GRG), government advisor Lawrence Tomlinson has told a Treasury Select Committee.
Tomlinson, who is an adviser to Britain's business secretary Vince Cable, said his dossier of cases against RBS's restructuring unit had "continued to grow" since he published his independent report into bank.
His report claimed that the 81% government-owned lender profited from struggling businesses which were pushed into default after being moved into the controversial unit.
Tomlinson claimed that by moving businesses into GRG, this can create more revenue for the bank through higher fees and margins.
It can also result in the purchase of devalued assets by its property division, West Register, he added.
Tomlinson told the committee that he was ready to hand the dossier over to the Financial Conduct Authority (FCA), in order for the watchdog to investigate, as the evidence he has collected revealed "morally wrong" practices.
However, he did add that there was no evidence of criminal misconduct.
Tomlinson runs LNT Group, based in the north of England which has annual revenue of £100m (€121m, $166m) and has interests in construction, software, car manufacturing, and care homes.
After the release of Tomlinson's report, RBS drafted in heavyweight lawyers to review the treatment of small-to-medium sized enterprises (SME) and denied wrongdoing.
RBS's newly installed chief executive, Ross McEwan, said the bank appointed Clifford Chance to help its inquiry into the treatment received by SMEs in financial distress.
"To ensure our customers can have full confidence in our commitment to them I have asked the law firm, Clifford Chance, to conduct an inquiry into this matter, reporting back to me in the new year," said McEwan.
Since then, the FCA kicked off its independent review of RBS's treatment of business customers in financial difficulty by appointing the Promontory Financial Group and Mazars to conduct the report.
It will also consider allegations of poor practice set out in the report by Tomlinson and referenced in Sir Andrew Large's report.
Meanwhile, Large, who was commissioned by RBS in 2013 to conduct a review, said Tomlinson's were not true despite previously citing poor business lending practices himself.
"There's an element of plausibility in the assertions that are in the Tomlinson report ... but that doesn't mean to say I think those activities are actually happening. I didn't have any evidence of them," said Large, a former deputy governor of the Bank, told parliament's Treasury Select Committee earlier this month.