More than 200,000 parents could be missing out on their full entitlement to the state pension by failing to claim child benefit, HMRC has warned in a letter to the Treasury Committee.
Parents of children under 12 who do not pay national insurance can receive national insurance credits to build up their state pension by registering for child benefit.
However, data from HMRC shows that of the 7.9 million households claiming child benefit, around 3% may not benefit from national insurance credits as the benefit is claimed by the higher earner.
The problem could affect households where one parent works and the other stays home to look after their children.
In response to the letter, Nicky Morgan MP, chair of the Treasury Committee, said the Treasury Committee had "long warned the Government" of the issue.
"Now we have an idea of the scale of this problem, the Government needs to pull its finger out and make sure people are aware of the issue and know how to put it right."
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