A businessman who wrote a government report that criticised RBS has been told he can no longer remain a customer of the bank, Panorama has learned.
In the 2013 report, Lawrence Tomlinson accused RBS of systematically wrecking viable businesses.
And in 2014, RBS deputy chief executive Chris Sullivan told him he would have to take his mortgage, business and personal accounts to another bank.
But RBS said the decision had nothing to do with the critical report.
Mr Tomlinson's report accused RBS of using questionable property valuations to artificially downgrade viable businesses.
He said the businesses had then been moved to the bank's Global Restructuring Group (GRG), which had charged extra interest and fees.
RBS denied GRG had treated customers unfairly. It commissioned its own inquiry, which rejected the main allegations in Mr Tomlinson's report.
But last June Mr Sullivan sent an email to Mr Tomlinson telling him to move his mortgage and all his bank accounts.
It said: "In view of your longstanding dissatisfaction with the bank, we have concluded that the required trust between you and the bank has irretrievably broken down.
"For that reason, we have concluded that we cannot continue a banking relationship with you either in a personal capacity or a corporate capacity."
The bank eventually backed down over the mortgage on his home, but Mr Tomlinson had to find new bankers for his business, which employs more than 2,000 people.
He said: "I've been with them 20 years. I've tried to help them change, and they've cancelled all my business and personal accounts - I think to just create the maximum amount of disruption to me and my businesses"
But RBS said trust had broken down because of a long-running dispute over a complaint Mr Tomlinson had made in early 2012. It said two investigations into this complaint had found no evidence of wrongdoing and that Mr Tomlinson had failed to attend a meeting to discuss the findings.
Panorama has also spoken to business people who accuse Lloyds Banking Group of using similar practices to those outlined in Mr Tomlinson's report.
Alison Loveday, a solicitor who acts for businesses in dispute with their banks, said Lloyds customers had also been shocked by low valuations.
"After examining a number of cases, we did coin the term 'the Lloyds effect' because we could see the valuations were hammering the property value down as much as 50%," she said.
Lloyds has also been accused of adding additional fees and interest when struggling companies are moved to its Business Support Unit.
But the bank said its fees were appropriate and it made no commercial sense to undervalue property.
It added the majority of customers who went into the Business Support Unit were helped back to financial health.
"More than two-thirds of customers get back to viability, to be treated like normal customers. That's over a thousand this year alone," Lloyds said.
But customer Ross Finch said the Business Support Unit had been anything but supportive and his hotel business had been charged an extra £298,000 in one year after being transferred to it.
Then, three years after being transferred to the unit, Mr Finch was suddenly dropped as a customer.
He said: "I got a phone call from one of the people that we'd been dealing with who said, 'I've got to read you a statement.' At which point, they said we are selling your loan, we expect the transaction to complete today."
He says his business was trading profitably: "This was a solid strong resilient business that had got through the recession and the difficult economic times."
Lloyds had sold his loan to a US private equity group called Cerberus. The hotel's overdraft with Lloyds ended, and Cerberus does not do overdrafts. Within months Mr Finch had to put the business into administration.
Lloyds said Mr Finch's allegations were untrue but details could not be discussed because of legal proceedings.
The hotel loan was just one of billions of pounds' worth of business loans that the bank has sold to Cerberus in the past two years.
Cerberus said Mr Finch's business was losing money and he did not present "a viable business plan". It added that it was "socially responsible" and provided "professional management".
Lloyds said it carefully approved companies buying loans and ensured they carried on treating customers as the terms of the loan allowed.
Stephen Pegge, from Lloyds, said: "We check to make sure that these organisations are doing the job that they're asked to do and that they do behave in a responsible way."
In a statement, the bank added: "Lloyds Banking Group refutes the BBC's suggestion that the practices of the group's Business Support Unit can, in some way, be compared to those identified in the Tomlinson report."
Watch Panorama: Did the Bank Wreck my Business? on BBC One, 24 November at 20:30 GMT or watch later on iPlayer.