The chairwoman of an influential committee of MPs has said it is "troubling" that cases brought to the Financial Ombudsman Service (FOS) by consumers may not have been decided correctly.
The ombudsman service has said an independent person will be appointed to carry out a review to better understand and address the concerns raised following a Channel 4 Dispatches investigation into the service.
Nicky Morgan, who chairs the Treasury Committee, said: "The FOS is essential in underpinning consumer confidence in the financial services industry, and in redressing the power imbalance between large financial institutions and their customers.
"It is troubling, therefore, that cases may not have been decided correctly."
Her comments follow the Dispatches investigation into the way complaints are being handled by the FOS, which has been dealing with surges in payment protection insurance (PPI) complaints in recent years.
The Dispatches programme suggested significant numbers of cases may need to be looked at again after finding evidence that staff with inadequate training or knowledge were deciding people's complaints against financial firms.
Concerns have also been raised that pressure to resolve cases quickly could have led to banks being wrongly favoured.
Following the investigation, Mrs Morgan wrote to Caroline Wayman, chief ombudsman and chief executive of the FOS.
In her response, Ms Wayman said that to "better understand and address the concerns raised by the programme, our non-executive board will be appointing an independent person to carry out a review".
Ms Wayman also said in her response: "We feel very strongly that the concerns voiced in the programme do not give a fair impression of the Financial Ombudsman Service when seen against the overall breadth and context of our work."
Responding to a question about whether the FOS has the ability to reopen cases, Ms Wayman said: "The circumstances in which we can reconsider a complaint are extremely limited.
"We may, however, consider the matter afresh if material new evidence subsequently becomes available which the ombudsman considers likely to affect the outcome.
"And as a public body, our decision-making is of course subject to judicial review - which means our decisions come under scrutiny by the courts."
Ms Wayman said since 2010, when the FOS started to see significant volumes of PPI complaints, it has found against banks in around two-thirds of cases.
She said on joining the service, all new case handlers take part in a comprehensive training programme.
Commenting on the correspondence, Mrs Morgan said: "The Dispatches programme raised concerns about the FOS's decision-making and governance.
"These have been echoed by correspondence received by the committee from current and former FOS employees, who have also expressed dismay about poor culture and low morale."
She continued: "As Ms Wayman says, it's right that cases be reopened if there is any new evidence that might affect the outcome. That must surely include failures in the FOS's own processes."
Mrs Morgan said the independent review must consider the FOS's approach to decision-making, the assurance process, and the causes of low staff morale.
She continued: "The committee will want sight of the terms of reference before they are finalised.
"The review should be demonstrably independent, all findings of the review should be published, and the committee will expect to take evidence from the reviewer."
Mrs Morgan said she will be writing to Ms Wayman to set out in more detail the committee's expectations of the review, and the committee will consider whether further action is required in response to the correspondence received.