Tens of thousands of pensioners may miss out on money owed from HMRC following a major state pension error, a leading campaigner has warned.

HMRC is in the process of tracking down more than 180,000 pensioners who may have been underpaid. Specifically, the issue largely affects mums who took time out of work to look after children and claimed Child Benefit between 1978 and 2000.

These people may be missing Home Responsibilities Protection (HRP) on their National Insurance record - as a result, it could mean they’ve been underpaid the state pension and could be owed money. HPR reduced the number of qualifying years you need to claim the state pension for parents and carers. It was replaced by National Insurance credits in 2010.

Child Benefit claim forms submitted before 2000 did not include a National Insurance number and this means the relevant HRP may not have been carried across correctly in some cases. HMRC has so far issued over a quarter of a million letters to those who may be affecting, encouraging them to put in a claim.

Have you been underpaid the state pension? Let us know: levi.winchester@reachplc.com

But former pensions minister Sir Steve Webb has warned that many people may be put off from acting as these letters only mention how to claim online. There is a paper claim form (CF411) which can be used instead.

Sir Steve Webb, who is now a partner at pension consultants LCP, said: “Whilst I understand the desire of government departments to cut costs, it is completely inappropriate to write letters to hundreds of thousands of pensioners which suggest that the only way to apply is online.

“I am concerned in particular for older pensioners who may not have friends or family to help them. Those who have been underpaid have typically missed out on thousands of pounds, and they deserve to have this put right. Unless HMRC addresses this issue it is highly likely that tens of thousands of older pensioners may continue to miss out on money which is rightfully theirs.”

Anyone who is affected could be owed an average of £5,000 each, with the DWP expecting to pay out more than £1billion in arrears. The DWP estimates 43,000 of those affected are now deceased but their family will be able to make a claim for any money owed. Those over pension age are being prioritised and contacted first.

An HMRC spokesperson said: "Contrary to what’s been claimed, the letters do include a helpline number to request a paper application form - although for most people it will be much quicker and easier to use our online service."

How do I check if I’ve been underpaid?

The main rules for qualifying for a year of HRP from 1978 are:

  • You had to be receiving child benefit in your own name (not that of a spouse or partner)

  • Your child was under 16 for the whole of the financial year in question

  • You were not paying the married woman’s ‘reduced stamp’

If you suspect you have missed out, you should first check your state pension and your National Insurance record. For those who reached pension age after April 5, 2010, any year of HRP/credits should be showing as a complete year on your National Insurance record. If not, then you may have missed out. The Government has also created an online checker tool on GOV.UK to see if you’re likely to be eligible to make a claim.