More than 12.2 million customers are expected to complete a tax return for the 2020/21 tax year, so this means about a third are still to get their paperwork in order.

Although HMRC is waiving penalty fees for late filing of tax returns and late payments for a month, taxpayers will still have to pay interest on the tax owed.

Anyone who cannot file their return by the 31 January deadline will not receive a late filing penalty if they file by 28 February. People who can’t pay their tax by the 31 January deadline will not receive a late payment penalty if they pay their tax in full, or set up a time to pay arrangement, by 1 April.

Myrtle Lloyd, HMRC’s director general for customer services, said: “We know some customers may struggle to meet the self-assessment deadline on 31 January which is why we have waived penalties for one month, giving them extra time to meet their obligations.

“And if anyone is worried about paying their tax bill, they can set up a monthly payment plan online – search ‘pay my self-assessment’ on GOV.UK.”

Kevin Sefton, CEO of personal tax app untied, said: “Even with the extra month, we believe that 700,000 people are in line to miss the filing deadline and will receive a £100 fine. HMRC has reported that it gets nearly 1,000 returns a day 14 months after the end of each annual deadline, and sometimes 500 a day 26 months after.

“The longer the delay in submitting the forms, the bigger the size of the penalties. We urge everyone to get any outstanding tax returns to HMRC as soon as possible and definitely before the end of February to avoid penalties. Taxes often feel overwhelming but the sooner you start, the better.”