Until recently, Carole Davies, 76, from Merstham in Surrey, was told she was entitled to less than £1 a week.
"When I retired in 2003, my state pension was so low - 40p a week - I was told that it would be paid once a year," she told BBC Radio 5 Live. "Despite my husband Michael questioning this after he retired in 2005, we were told I wasn't due anything more."
Mrs Davies, a stay-at-home mum who worked in an administrative role for only a short period of time, had built up almost no entitlement to a state pension in her own right, as she had not built up enough National Insurance (NI) contributions. Every week, for more than 15 years, she had been underpaid, not knowing she was actually eligible to a married woman's pension.
After watching a TV programme about pensions in November, she decided to contact the Department for Work and Pensions (DWP) again, convinced she should be getting more. Earlier this year, she finally got an answer - the grandmother of eight is owed £61,000 and is entitled to £82.45 per week.
In March, documents revealed in the Budget showed an estimated 200,000 pensioners could be collectively owed up to £3bn after the under-payment of state pensions for decades.
A review, involving a team of more than 100 civil servants, is taking place to trace all the women who have been affected by systemic failures to automatically award pension pay rises, stretching back to 1992. The process could take up to five years. Ms Davies is among 5,000 women entitled to potentially huge refunds, many of whom will not be captured by the DWP's search, due to a rule change in 2008.
Former pensions minister and partner at Lane Clark and Peacock LLP, Steve Webb, first highlighted the problem and the scale of the underpayments. He told the BBC that under a little-known rule, the women who qualify for this concession are those who are getting a tiny amount of what is known as "graduated retirement benefit" (GRB) under the old state pension system, which ran until 1975.
The average amount they are receiving is around £1.24 per week, but this is enough to qualify for a married woman's pension. They can backdate their claims to their husband's 65th birthday and could be in line for tens of thousands of pounds. It is incredible that there are thousands of women getting such tiny pensions, but even more incredible that many could potentially be entitled to tens of thousands in back payments," said Mr Webb. "It is as if they are sitting on unclaimed winning lottery tickets. It is very important that women on these very small pensions make contact with the DWP as soon as possible to see if they could be entitled to a windfall".
Unlike in other cases, this boosted payment is not automatic and women have to claim for it
. That means many women know nothing about it and have missed out on this increase for years.