From 1978 parents who take time off work to care for their children have been granted National Insurance credits for those years to make up for any gaps in their National Insurance record. The system was originally called Home Responsibilities Protection (HRP).

HRP allowed parents to build up entitlement to the state pension despite not working.
 
National Insurance Credits for parents and carers replaced HRP from 6 April 2010.
 
Since April 2016 the full state pension is only paid out to those who have at least 35 years of full National Insurance contributions. Anyone with less than 35 years qualifying years (or NI credits) won’t receive the full amount.
 
 However, it has been discovered that the system in place hasn’t accurately recorded  HRP credits for some mothers, and in some cases women who took time out of work to raise children have been underpaid their State Pension over the course of their retirement.
 
The Government has confirmed this newly discovered error is the second-largest source of mistakes in the payment of state pension, behind the £1.5bn underpayment to married women and widows.
 
The Department of Work and Pensions (DWP) is working with HM Revenue & Customs to assess how many people have been affected and how much they have been wrongly denied.
 
If you received HRP between 1978 and 2010 we would urge you to check your National Insurance record to ensure you received the correct NI credits due. Please go to the GOV.UK website to check; https://www.gov.uk/check-na...
 
Unfortunately Usdaw does not have access to your State Pension records so if you want to check if you are owed any money contact:
Pension Service on 0800 731 0469 (option 2, then option 4).