An error dating back decades has left hundreds of thousands of people underpaid a combined total of more than £1billion in state pensions.

In a new report by the public accounts watchdog it was revealed that more than 200,000 pensioners were left “out of pocket" by the Government.

The Department for Works and Pensions (DWP) estimates 210,000 people have been affected by the mistake.

The total underpayment amounts to £1.3bn, which averages around £5,000 per person.

According to the report, the error is due to missing Home Responsibilities Protection data.

This was a scheme which ran between 1978 and 2010 to help protect parents’ and carers’ state pension.

A DWP spokesperson said: “The action we are taking now is correcting historical underpayments made by successive governments.

“Our priority is ensuring pensioners receive the financial support to which they are entitled and we have set up a dedicated team and devoted significant resources towards completing the correction exercise.”

But, an inquiry by the Public Accounts Committee (PAC) found that identifying those affected will be difficult, as the government no longer holds the relevant records.

Chairman MP Meg Hillier said: “Many pensioners have been left significantly out of pocket by up to thousands, while DWP has been asleep at the switch. These are injustices that may never be corrected for some.”

The watchdog said there are “serious doubts over whether the state pension is being paid accurately”.

The criticism follows another previous underpayment of £2.37 billion affecting 237,000 pensioners who are mainly married, widowed or over 80, as reported last year.

The DWP says following repayments, these figures are now down to £1.2bn affecting 165,000.

The PAC says there is concern that “similar errors may occur with other benefits and for the lack of assurance that further historic underpayments may not occur in future”.

Hillier added: “We expect DWP to respond to our report in a timely fashion, but frankly, paying pension accurately is a basic that we expect from DWP and not recommendations that our committee ought to be having to make.”

The DWP says their priority is ensuring pensioners receive the financial support to which they are entitled and where errors do occur are committed to fixing them as quickly as possible.

“We have always made clear that we would continually review the estimated numbers affected and cost of the exercise as more information became available,” a spokesman said.

“State pension underpayment rates remain low at 0.5% of expenditure.”

It also claims they have now reviewed more than 590,000 cases as part of the exercise.

If you believe you have been affected by this issue, you can contact the pension service by phone or post.

Contact details can be found on their website here.

Helpline hours may vary during the Christmas period.