"There are instances where additional confidential information was contained within the description of the complaint"
The FCA has admitted to publishing confidential information about people making complaints against the regulator.
In response to a Freedom of Information Act request published on its website in November 2019, the FCA said "certain underlying confidential information may have been accessible".
The response related to the number and nature of new complaints made against the FCA and handled by the Complaints Team between 2 January 2018 and 17 July 2019.
The FCA says the publication of this information was a mistake and remove the relevant data as soon as it became aware.
It has since undertaken a full review to identify the extent of any information that may have been accessible.
In a statement, the FCA said: "Our primary concern is to ensure the protection and safeguarding of individuals who may be identifiable from the data.
"In many instances, the extent of the accessible information was only the name of the person making the complaint, with no further confidential details or specific details of their complaint.
"However, there are instances where additional confidential information was contained within the description of the complaint, for example an address, telephone number, or other information. Where this is the case, we are making direct contact with the individuals concerned to apologise and to advise them of the extent of the data disclosed and what the next steps might be."
No financial, payment card, passport or other identity information were included in the breach and the FCA has referred the matter to the Information Commissioner’s Office.