According to reports, the Inland Revenue's NIRS2 computer system has been overpaying rebates via pension funds to thousands of savers who have opted out of the state earnings related pension system for almost five years.

The mistake is said to have arisen because the ill-fated computer system failed to register that some employers were sending in duplicate information about their employees, and mistakenly counted the information twice.

The Revenue has demanded that the insurers return the overpayments, but it is feared the cash could be worth 40% less as it would have been invested into plunging stock markets.