Women who divorced later in their lives may be unknowingly missing out on thousands in extra state pension money.
Married women are entitled to the equivalent of 60 per cent of their husband's basic rate, provided they reached state pension age prior to April 2016.
The "married woman's rate" is worth £80.45 a week, and is available to married women who did not earn a larger pension in their own right. A separate provision covers those who retire after that date.
If divorced, however, a claim of up to 100 per cent of the husband's pension to compensate for a loss in household income following the separation can be made.
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The rate is based on an ex-husband's National Insurance contributions up to the date of divorce. That means if a woman divorces her husband after he retired on a full pension, she can claim a full basic state pension worth £134.25 a week.
Divorcees could lose out on around £50,000 over a 20 year retirement through failure to claim the full amount, and new analysis shows that around 100,000 divorced women are not claiming.
Back payments worth thousands of pounds
Former pensions minister Sir Steve Webb, who conducted the analysis, found that thousands of divorcees, widows and married women were not aware they could claim a state pension based on their husband's records.
Since then, many have secured back payments worth thousands, while others have had their pensions increased.
If a woman is already collecting her pension at the time of divorce, she must inform the Department for Work and Pensions (DWP) in order to claim the increased rate.
If a divorcee remarries before collecting their state pension, the rate is based on their new husband's record. But, if they remarry after collecting their pension, the amount will not change.
Experts are saying that more should be done to raise awareness among women of the entitlement, with even some DWP staff unaware of the rules.
A DWP spokesman said pensioners are urged to report changes of circumstances - such as divorce - in leaflets that get sent out every year.
He also said, "DWP has dedicated, trained teams for handling all contacts from customers asking us to check their pension entitlement."
A petition by Sir Webb urging the DWP to find women who have been underpaid has been set up, and can be signed here: petition.parliament.uk/petitions/334388