More than 1 million people have missed the deadline to file self-assessment tax returns with HM Revenue & Customs (HMRC), according to official figures.

Taxpayers had until midnight on January 31 to submit their returns online.

HMRC confirmed that 11.5 million people met the deadline, but 1.1 million returns remain outstanding.

Those who failed to file on time face an initial fixed penalty of £100, even if no tax is due.

Penalties will increase if the returns remain unfiled for three, six, and twelve months.

The HMRC estimates that these penalties could generate an additional £110 million.

On deadline day, 732,498 people filed their returns, including 31,442 who submitted them in the final hour.

Changes in tax policies, including the freezing of personal tax thresholds and high returns on savings, have contributed to a rise in first-time filers, with many unaware of their obligation to file.

Myrtle Lloyd, HMRC’s Director General for Customer Services, urged late filers to submit their returns promptly to avoid additional fines.

After three months, a daily charge of £10 can accrue up to £900, with further penalties of £300 or 5% of the total tax bill applied after six and twelve months, whichever is greater.

While an IT outage at Barclays may have affected some customers’ ability to pay, HMRC confirmed that late payment fines will not be applied until March 1.