Thousands of retired women could receive payouts from the Department for Work and Pensions (DWP) to make up for losses in their pension over two decades.
Around 200,000 people on the "old" state pension could be in line for payouts averaging £13,500 after being underpaid for 20 years.
The DWP said the errors focus on automatic cash increases for certain married women, widows and over-80s dating back to 1992 with "enhanced" pensions.
It estimated the bill for tackling the shortfalls to be about £2.7billion. The scale of the underpayments came to light in the details of a report by fiscal watchdog the Office of Budget Responsibility (OBR) report which was published alongside the Budget.
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