The National Audit Office has slated HM Revenue & Customs, the Pensions, Disability and Carers Service and five other public sector pension schemes, which have been involved in a £90m pensions blunder as 'entirely avoidable'. Some 85,000 retired professionals were overpaid by £90.2m through their pension while a further 4,917 individuals were underpaid by £191,000, yet these figures could rise as the schemes are still working through 26,000 more cases. The NAO said the administration of the schemes was 'complex and fragmented' and 'prone to error' as no one group was held responsible for its processing. The problems arose in the pension schemes because they did not have Guaranteed Minimum Pension information for some members, which meant that the bodies did not set accurate annual cost of living increases. The NAO said that the involved parties should have worked together to have prevented the error, The Daily Express reports. In some cases, the mistakes has gone undetected for 20 years as issues had been raised in the 1990s about problems with the scheme's administration, but a lack of action meant it went unresolved.