Money-saving expert Martin Lewis has said pensioners could be missing out on claiming a substantial money benefit.
He has spoken out to alert people to a pension calculation error that has left more than 200,000 people underpaid.
Mr Lewis appeared on Good Morning Britain on Wednesday to raise awareness of the issue, which he said has mostly affected female pensioners over the age of 66.
He said caregivers who took time off work between 1978 and 2010 because of childcare responsibilities may have had their national insurance miscalculated because home responsibilities protections – a previous scheme designed to protect parents’ and carers’ state pension – was not included.
Those affected should receive a letter in the post explaining the mistake and offering a payout worth “tens of thousands of pounds” but he fears people will see the letter and immediately think it is a scam.
He said: “Do not bin the letter. I'm going to keep it really simple. Hundreds of thousands of people aged over 66, mostly women, who took time off work for childcare responsibilities between 1978 and 2010 may have had their national insurance miscalculated because they may have been eligible for what’s called home responsibilities protection, where they should have got national insurances credit and they didn’t.
“To correct the error, the Government has started to contact individuals who missed out on the payment to inform them that they are due the credits.
“They're starting with letters to the over-66s: they're being sent as we speak. They might be sent over the next couple of weeks, so if you've not gone one yet, don't worry.
“My warning is do not bin the letter. These are not scams. If you get a letter from HMRC and it talks about home responsibilities protection, it is not a scam.
“Some scammer might try a trick on the back of hearing me say this, so you can also go direct to gov.uk.
“It really just is a heads up for people to watch out for the letter. Hundreds of thousands of people will receive one.”
A Government spokesman said: “We have identified and are correcting an issue related to the historical recording of home responsibilities protection on the National Insurance records for people who first claimed child benefit before May 2000.
“Most people's records will be unaffected, and we have launched a new online tool to help people check whether they need to claim. HMRC has begun writing to those likely to be affected.
“State pension underpayment rates are very low but where errors do occur, we are committed to fixing them as quickly as possible.
“The letters will be sent nationally and in phases, in order of how close customers are to state pension age. Those over state pension age will be contacted first.
“We will be taking a test and learn approach and aim to write to several hundred thousand people over the next 18 months.”
