By Kevin Peachey
Personal finance correspondent, BBC News
image copyrightBernie Weallansimage captionBernie Weallans with husband Martin and her children
Bernie Weallans had a nagging feeling she was owed something from the state pension system.
The 73-year-old, who worked in the oil industry, did not qualify for a pension in her own right as most of her paid work was outside of the UK.
But having been married to British husband Martin, 70, for more than 40 years, she was actually entitled to a married woman's state pension when he retired.
She received nothing. Now she will get a regular pension of £82 a week, plus £20,000 in arrears for the pension which she missed out on.
"This extra money will enable me to do more to support my children and grandchildren," she said.
"I would encourage any other woman who is not getting a pension to check whether she is entitled to anything."
Mrs Weallans, who was born in the Netherlands and now lives in Brighton, had contacted former pensions minister Steve Webb, now a partner at consultancy firm LCP, after seeing recent coverage of underpayment of pensions to women.
His research suggests that at least 100,000 people are entitled to some state pension, but are receiving nothing at all.
According to population estimates, 8.78 million people across Britain are aged 70 or over, but 8.53 million receive a state pension.
Some of those 250,000 may receive nothing because they have deferred retirement, have insufficient national insurance contributions, or are on certain benefits that exclude them from state pension entitlement.
LCP claims that many with a poor national insurance record may still be entitled to a pension, but have never claimed it.
Married women, such as Mrs Weallans, can claim a 60% basic pension based on their husband's contributions.
Others, from the age of 80, can claim a pension that should be paid regardless of national insurance contributions, after clearing a residence test.
image copyrightGetty Images
LCP said a large proportion of about 107,000 people (65,000 women and 42,000 men), who are aged 80 or over but have zero state pension, could claim this so-called category D state pension.
Mr Webb said some would not have claimed owing to language or health barriers, while others may simply be unaware of their entitlement.
"It is shocking that there are so many older people who are getting no state pension at all," he said.
"In particular, when we have a special state pension payable to those over 80 which does not depend on national insurance contributions, it is hard to understand why over 100,000 people over 80 are still on zero pensions.
"The government needs to do much more to identify those who are on zero state pensions and to make sure that they draw the pension to which they are entitled."
'Check for a claim'
He accepted that these non-claimants may have been "invisible" to ministers, such as himself in the past.
"One reason why successive ministers have failed to reach these groups is that they draw no pension and are completely outside the system so don't appear in official figures. This is a reminder to all in office to remember those who may be missing out altogether," he said.
If those aged 80 or over claimed their £82.45 per week, this would cost more than £400m a year in extra state pension payments.
A Department for Work and Pensions spokesman said: "We want everyone to claim the benefits to which they may be entitled and we urge anyone of state pension age, or their family and friends, to check if they are missing out on financial support.
"Anyone that thinks they may be eligible to receive a state pension can find out how to apply via Gov.uk."