HMRC is to give refunds to millions of retirees who paid too much tax on their state pension.

The taxman confirmed approximately 3.2 million people in the UK were in line for a rebate after an overcharging error dating back to at least 2016.

However, the chief executive of HMRC, John-Paul Marks, has only committed to automatically repaying pensioners who have been wrongly paying into the Government coffers since 2020.

Anyone who believes they wrongly paid tax before the start of the decade will have to prove they handed over too much of their money.

Marks said in a letter to MPs on the powerful Treasury select committee: “I am sorry that this error occurred and recognise the impact on affected customers.

“We will also conclude an internal audit review, ensuring the lessons are identified and applied in future.”

The average rebate is due to be worth approximately just £6 to each person impacted, totalling an estimated £19million.

HMRC overcharged pensioners due to a failure to take into account the rise in the state pension each year.

The triple lock policy – which has been in place since the coalition government – means state pension payments rise each April by the highest out of inflation, average earnings, or 2.5 per cent.

However, for at least a decade, HMRC has overcharged pensioners for one week of the year, taxing them at the annual increase, despite retirees still receiving the previous year’s lower payment rate.

HMRC first became aware of the problem two years ago but failed to act, although there is evidence of the problem dating back to at least 2016.

Marks added in his letter: “If customers believe they were affected in earlier years and have the necessary evidence, they can ask HMRC to review their position.

“These requests will be considered on a case-by-case basis.”

The civil servant said automatic repayments were only available from the April 2020 tax year because it was the “maximum period for which the available data enables us to identify and correct cases reliably and efficiently”.

When the issue first arose earlier this year, HMRC said it hoped to fix the problem by the end of the summer.

Reacting to the refusal of the taxman to automatically include overcharged taxpayers from before 2020, Antonia Stokes, of Low Incomes Tax Reform Group, said: “It is disappointing that HMRC data constraints prevent automated repayments further back, but it is positive that taxpayers can take steps to rectify earlier years if they identify they have been overcharged.

“HMRC should ensure they make this process as easy as possible and that they draw attention to its existence so that people can check entitlement for earlier years.”

The development comes after HMRC said it will have to perform a manual check on 100,000 tax calculations for the last year amid concerns it may have overcharged.

A computer error means that a check has had to be performed every year since 2021 for officials to issue refunds to Brits who have wrongly been made to pay excessively into the system.

READ MORE: State pension tax warning with one million Brits at risk