Thousands of pensioners could be due back payments worth as much as £10,000 following a state pension mistake.
The Department for Work and Pensions (DWP) error has been blamed on an IT issue and the complexity of the rules.
Latest figures, released in November, show more than 30,000 underpayments, worth more than £200m in total, were identified between January 2021 and October 2022.
While estimates state that as many as 237,000 pensioners could have been affected by the error, meaning more than £1.4billion could be owed.
The issue mainly impacts women who reached state pension age before April 2016, but three groups have been identified by the DWP as potentially being affected.
The first group is married women who should have received an upgrade of 60% basic state pension when their husband retired, with the average payments owed to this group totalling nearly £7,000.
The second group includes those over the age of 80 who were already in receipt of state pension when turning 80.
They should have automatically been upgraded to a 60% basic state pension at this point, with the average payment owed to them totalling £3,172.
While the third group is made up of people who should have inherited an enhanced state pension when their husband or wife died. On average, these people are owed £10,772.
Anyone who has been affected by the error will be contacted by the DWP once their case has been evaluated.
However, if you believe you are owed pension back payments you should contact the Pension Service by calling 0800 731 0469, or visiting the Gov.uk website.
The Pension Service will be able to find out if you are eligible for a state pension refund.
You should not contact the DWP.
