When the automatic renewal notices were sent out, 1.2 million of them did not include income details which are usually clearly stated on the document. 

HMRC has subsequently sent out follow-up letters which contained the income details used in its tax credits calculations. The tax authority blamed the mistake on human error. 

HMRC has apologised for the error but said that the missing information had not affected the calculations made for proposed payments, BBC News reports.

Recipients of the notices are being urged to carefully check their annual renewal.

An HMRC spokesperson said: “We are sorry that this happened, and for any inconvenience caused. We want to make sure we have paid customers the correct amount.

“A significant proportion of these customers are self-employed, and we need to confirm their previous tax year’s income has been correctly accounted for and to make sure they don’t miss the opportunity to give us an estimate if they are not certain about their income for this year.”