Millions of Brits are about to get a £100 fine through the post

Residents in every corner of the United Kingdom are being warned about a £100 fine coming their way if they don't act fast.

January is tough enough as it is, with the gap between Christmas and first payday of the year feeling like an absolute age and a half.

Well, things could get worse if you don't do the boring stuff that is required at the start of a new year.

In this case, we're talking about ending up with a hefty fine if you don't listen to HM Revenue and Customs (HMRC).

HMRC warning explained

HMRC, or the 'bloody taxman' as you're more likely to refer to it under muttered breath when reading your payslip deductions, is behind the advice and subsequent warning issued this month.

Now, as February approaches, HMRC has warned that Brits have just days to get their ducks in a row or face the penalty issued by them.

It's all to do with self-assessment tax returns.

And while it is a group of words that is enough to send most people to sleep, it's incredibly important to get it done.

Self-assessment tax returns are filed every January (Getty Stock Images)

Late payment

The deadline for filing your self-assessment tax returns to HMRC is the end of the month which is this Friday (31 January).

Miss this deadline and you'll find yourself facing a HMRC penalty, something no ones wants amid the years-long cost of living crisis.

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.

"After that, you'll have three months of breathing space before HMRC issues daily penalties of £10, up to a maximum of £900, with fines getting more severe after that."

The forms must be filled out if you're self employed or have a side hustle to a main job where you've earned more than £1,000 (Getty Stock Images)

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

You'll need to file a self-assessment tax return if you are self-employed.

Even if you are employed and get your wage via PAYE - where tax is deducted automatically on your payslip - those with a side hustle will need to check if they need to file one.

So if you've had a successful year on Vinted, and your extra cash was more than £1,000 (the tax-free allowance per year), you'll need to get the paperwork filled out.

On top of the £100, there will also be a 7.25 percent charge on any late payment. So if your bill is big, it's going to get a whole lot bigger.