With just a week until the Self Assessment deadline of January 31, 3.8 million people still haven't filed their tax returns.

And if they don't get on with it, they risk a £100 penalty.

HM Revenue and Customs (HMRC) is expecting more than 12.1 million tax returns to be filed for the 2022 to 2023 tax year, along with any payment that is owed. To date more than 8.3 million online returns have been received.

Myrtle Lloyd, HMRC's director general for customer services, said: "If you are a Self Assessment taxpayer, now is the time to take action and get your return done. People can familiarise themselves with the process by checking out HMRC's online resources on GOV.UK.

"Once a tax return is submitted, it's easy to find out what's owed and to pay online or using the HMRC app. Just search 'pay my Self Assessment' on GOV.UK to find out more."

Anyone unable to pay in full may be able to set up a Time to Pay arrangement and can find out how to do this online, without speaking to HMRC, if they owe less than £30,000.

The penalties for late tax returns are:

• An initial £100 fixed penalty, which applies even if there is no tax to pay

• After three months, additional daily penalties of £10 per day, up to a maximum of £900

• After six months, a further penalty of 5% of the tax due or £300, whichever is greater

HMRC will consider a customer's reasons for not being able to meet the deadline. Those who provide a reasonable excuse may avoid a penalty.

Anyone who thinks they no longer need to complete a Self Assessment tax return for the 2022 to 2023 tax year should tell HMRC - so that they can issue a withdrawal notice - before the deadline on January 31 to avoid any penalties.