State pensioners have been urged to check if they qualify for an income boost as hundreds or thousands are estimated to have been underpaid.

Home Responsibilities Protection (HRP) was a scheme designed to help protect the state pension of parents and carers. It ran from April 6, 1978, until April 5, 2010, when it was then replaced by National Insurance (NI) credits.

People received HRP automatically if they claimed Child Benefit for a child under 16, or Income Support because they were looking after a sick or disabled person and were not available for work.

However, after the benefit was replaced with NI credits, it has since been discovered that the system failed to accurately record HRP credits for some claimants. As a result, people – largely women – who took time of out work to raise children or care for people have been underpaid their state pension.

This underpayment occurred because missing HRP credits reduced their National Insurance contributions record, which is used to calculate state pension entitlement. People typically need around 35 years of NI contributions to get the full state pension rate.

Iona Bain, BBC Live Morning money expert, told viewers on the show today: “We’re talking about 370,000 people at least who could be owed money, and it only has come to light in recent years that this underpayment has been going on. That’s why the Government has been writing to people since last autumn to let them know they may be underpaid and they can apply for this money now.

Ms Bain added: “The great thing here is that we have already started to see some people get this money through and hopefully it’s going to make a big difference.

“But the message is there are still lots and lots of people who have missed out and, in particular, if you are a woman in your 60s or 70s, you might want to pay attention here. If you’ve got a letter, please don’t chuck it away – don’t ignore it.

“And if you haven’t got the letter, that doesn’t mean that you’re not eligible. You should still go on HMRC‘s website and check whether you’re eligible, because you could be in for a tidy sum.”

The show then aired two success stories of women who have received backdated state pension payments.

One viewer, Maria, explained how she received a letter from HMRC indicating that she may be eligible for money. She said: “I followed it up and subsequently received a backpayment and an increase in my state pension. I cannot thank Iona and the team enough for flagging this up and would encourage anyone contacted to respond.”

Sandy, who didn’t initially receive a letter, took matters into her own hands after watching the BBC show and was also successful. She explained: “Iona first mentioned Home Responsibilities Protection earlier this year. I’d never heard of it, so I went online and completed the HMRC form.

“After about three months, I was notified that I was owed £1,909, plus a small increase on my monthly state pension. So many, many thanks, iona. It’s going to be a very good Christmas.”

Ms Bain continued: “The women mentioned two different ways there. How can everyone else check if they’re eligible? Well, Maria and Sandy have both illustrated that you may get a letter but you may not do, and that’s a really important point to highlight.

The money expert said HMRC is writing to everyone that it thinks is affected by this, however, she warned: “It’s only using the addresses that it has on file, which means that some people may not have that correct address. They may have moved house, and that’s why it’s really important to check online.”

Outline the “main criteria”, Ms Bain said: “Did you put your National Insurance number on those forms back in the day? if you can’t remember, it may be more helpful to think about whether you fit into the broader criteria of people that might have been affected by this issue.

“If you were claiming child benefit for a child under 16, or you were caring for a child with your partner who claimed child benefit instead of you, you may be eligible, and let’s not forget as well those who were looking after those who are sick or disabled.

“If you were receiving income support or that individual was claiming benefits and you may be eligible as well. Bear in mind that if you made your first claim for child benefit after May 2000, then this won’t affect you, because after that point you had to put your National Insurance number on the forms. So really we’re talking about those who made their first claim prior to 2000.”

She added: “You might be thinking well, surely the Government can just check its records, figure out who’s eligible and then write to everyone who’s affected. But the problem is that Child Benefit records are actually deleted five years after the first claim is made, so it’s just not possible to know everyone who’s affected.”

Sharing a couple of other factors that may deem a person eligible, Ms Bain said: “If you were a foster carer for a full tax year between 2003 and 2010, you may also be eligible for HRP, and that also applies for those who were caring for a friend or family member’s child in Scotland, otherwise known as a kinship carer.

“The main group of people affected by this are women, but not exclusively. So if you are a chap who’s over the age of 80; if you get a state pension of less than £85 a week and you took time off to look after a child or someone who was sick, then you also need to check.”

Morning Live airs on weekday mornings between 9.30 am and 10.45 am on BBC One.