An extra 105,000 extra State Pensioners have been underpaid, new figures reveal - most of them women.
The issue affects many people getting the 'old' State Pension, which is paid to people who reached State Pension age before April 6, 2016.
Many of these people on low pensions were allowed to claim a 60% their State Pension if their spouse or civil partner had paid higher National Insurance contributions.
Due to the social norms of previous decades, men almost always earned more than women - and this is often still the case.
What this means in practice is that 80% of the people claiming this perk were women relying on their husband's higher contributions.
Have you been affected by the State Pension underpayments? Let us know: mirror.money.saving@mirror.co.uk
But a mistake at the Department for Work and Pensions (DWP) meant many were not given the top-up, dating back to 1985.
The DWP has been going back and correcting its mistake, but new figures from the National Audit Office (NAO) show that the problem is bigger than expected.
The DWP previously thought it had underpaid 134,000 pensioners more than £1billion.
But the latest figure is 237,000 people underpaid almost £1.5billion - and the real figure could be even higher.
The DWP previously thought fixing the problem would cost between £620million and £2.8billion.
The NAO said: "The Department became aware of potential issues with underpayment of State Pension entitlements in Spring 2020 after a series of cases involving official error were highlighted in the media
"In 2021-22 the Department has refined its best estimate by performing the additional scans of its pension systems that it was unable to do last year due to planned system upgrades."
The NAO added that the DWP thinks it "underpaid £1.46billion to 237,000 pensioners" and "will need to review around 700,000 potentially affected cases".
Much of the mistakes were discovered by former pensions minister Sir Steve Webb, now a partner at Lane, Clark and Peacock.
On Twitter, Webb said he raised the issue with the DWP as far back as 2008.
He added: "DWP also admit that state pension correction exercise will have to be extended to 'late 2024' (against 'end 2023') as previously planned."
Others who missed out include pensioners who should have been paid the minimum 60% of the basic state pension after they turned 80.
The DWP is prioritising individuals who fall into "at risk" categories, such as those who are widowed or aged over 80.
A DWP spokesperson said: “The action we are taking now will correct historical underpayments made by successive Governments. We are fully committed to addressing these errors, not identified under previous governments, as quickly as possible.
"We have set up a dedicated team and devoted significant resources towards completing this, with further resources being allocated throughout 2022 and 2023 towards the underpayments exercise."
How to check if there's a shortfall on your pension
The DWP says those whose husband became entitled to their pension on or after March 17, 2008, do not need to take any action and will be contacted.
To check if you’ve been underpaid, you can use this online calculator created by Lane Clark & Peacock.
You can also check how much you are being paid by monitoring your bank account or annual State Pension statement.
If you think you have not had the correct state pension amount for any other reason, you should contact the Pensions Service arm of the DWP directly.
You can call on 0800 731 0469, but be aware that the lines are only open from 9.30am to 3.30pm Monday to Friday.
