Aviva overcharged 13,000 pension plan holders by an average of £250, the Telegraph reports.
The insurance company, which has since apologised for the error and repaid the £3.25m owed to customers, says the error affected less than 0.5 per cent of policyholders.
A spokesman says all 13,00 policies have been amended in the past two weeks. He says: “Two sets of policy fees were levied on some policies, and these are mainly ex-Commercial Union and CGU policies. It’s very regrettable and we’re very sorry this has happened.”