Millions of Brits given one-day deadline to avoid £100 fine through the post

Residents all over the country are at risk of being handed a fine for failing to do one simple thing.

We're at the end of January, which may come as a relief to many who have been limping to payday since their Christmas payday.

However, your financial woes may not be over just yet as there's more admin work that needs doing in what feels like the longest month of the year.

Messages from HM Revenue and Customs (HMRC) have been sent out to Brits who may have forgotten to tick this one off their January checklist.

It's all to do with submitting your tax returns, which may sound like the most mundane thing ever, but failing to do so could result in a hefty fine being posted through your letterbox.

Nobody likes doing their taxes, but we have to (Getty Stock Image)

What warning has HMRC issued?

You're familiar with the taxman - they're responsible for those chunky deductions you get on your payslip.

They're behind the advice and warning which has been issued this month, urging Brits to pay up or risk penalties, which could bog you down for up to a year after the deadline.

With February on the horizon, working individuals will have just one day to make sure they've got their forms in place to file their self-assessment tax returns.

It isn't the most exciting thing, but it's crucial that you get this done before the self-assessment deadline this Saturday (31 January).

Calculating the amount your owe can be a headache, but it's always worth it (Getty Stock Image)

What happens if you pay late?

If you miss the deadline, you'll be handed an instant penalty by HMRC, which is less than ideal in the ongoing cost of living crisis, which shows no sign of slowing down.

According to the official government website, these are the penalties you may face for filing a late tax return as time goes on:

• A £100 penalty
• After 3 months, daily penalties of £10 per day, up to a maximum of £900
• After 6 months, another penalty of 5 percent of the tax due or £300, whichever is greater
• After 12 months, another 5 percent or £300 charge, whichever is greater

Speaking last year, Alastair Douglas, CEO of TotallyMoney, said: "With Friday's deadline fast approaching, it's important to get your tax return filed as soon as possible - and even if there's nothing to pay.

"That's because the taxman will be waiting to dish out £100 fines as soon as the clock strikes midnight."

You could lose a chunk of your earnings if you forget to file your return on time (Getty Stock Image)

Do I need to file a self-assessment tax return?

If you are self-employed, you will need to file a self-assessment tax return.

Those who are employed and get their wage via PAYE, with tax automatically deducted on your payslip, may be in the clear - unless there's a side hustle to account for.

This can be as simple as having a uber-successful past year on Vinted or eBay.

If your extra earnings add up to more than £1,000 (the tax-free allowance per year), law states that you must fill the return out, and submit it to HMRC.

As well as the initial £100 penalty, a 7.25 percent charge will be applied to any late payment.

It's best to file everything on time because if your bill is large, your fine will be a lot bigger than you may think.