"The shortcomings not only affect individual complainants – sometimes very significantly – but also have the potential to undermine confidence in the regulatory system."
In response to the commissioner's report the FCA said a "high percentage" of complainants had received "timely and adequate responses", but acknowledged it was "unacceptable" some complainants had experienced significant delays or received inadequate responses.
The FCA said it was due to publish a consultation paper on proposed changes to its complaints scheme, including proposals to make it "more readily understandable" to complainants and clarify its position on compensation.
The regulator said: "During the course of this year, we have implemented comprehensive steps to eliminate the backlogs in complaints handling and improve performance.
"We are pleased that the commissioner is already seeing signs of improvement."
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