RBS owned insurance companies Direct Line and Churchill has been fined for tampering with files.
The files in question are customer compaint files which had been submitted to the Financial Services Authority (FSA).
They have been fined £2.17m, however the FSA have said the changes were small and would not effect customers.
The action is a major breach in rules.
Tracey McDermott of the FSA said: “The firms failed to give clear instructions resulting in staff making inappropriate alterations with one individual even forging the signatures of colleagues.
“The firms’ management did not know what changes had been made or when [but] it is of critical importance that material provided to the FSA must reflect the picture as it is – not as they might like it to be,” she added.
The tampering occurred when insurers tried to sort out the FSA’s continuing enquires, which began three years ago, looking into the approach taken by financial firms when dealing with customer complaints.
Only a year ago RBS itself was fined for inadequately dealing with customer complaints, to the sum of £2.8m.
Direct Line and Churchill both looked into closed complaints and staff were told the complaints must pass.
When the FSA received their sample 50 files in April last year it was told that some may have been altered or “created”.
Further investigation revealed 27 out of 50 had been altered, with seven containing forged signatures.
“In this case, the alterations did not impact on the FSA’s ability to do our job,” the FSA said.