The Government was late in paying £1.5bn to UK pension companies at the height of the crisis over the Nirs2 National Insurance computer system in 1997 and 1998.
The Association of British Insurers told Computer Weekly of the shortfall after social security minister Jeff Rooker admitted, in a parliamentary written answer, that the Government had paid £44.3m in compensation to pension companies for late payment of age-related rebates for the 1997/98 tax year.
A spokesman for the association said, "We were very unhappy about the potential losses to our members. And the compensation paid - 3% to 4% - is not a very high rate of return."
The Benefits Agency is still reviewing Retirement Pension claims affected by the delayed implementation of Nirs2, but hopes to complete the process by the end of this year.
According to Rooker, about 130,000 pension cases have still to be reviewed.
In addition, Rooker said £52,215 has been paid to insurance companies for work they undertook to modify their IT systems. The work was necessary to minimise the impact that incorrect payments of rebates generated by Nirs2 would have on their customers' investments.