"A wasp in my car caused me to have an accident and my tax return, which was inside, was destroyed", one taxpayer claimed was the reason behind filing self-assessment late last year.

That's just one of several far-fetched excuses used in attempts to avoid a HMRC penalty, but a technical glitch with the Revenue's systems saw many at risk of being fined recently.

The latest issue arrives hot on the heels of a previous error with HMRC's systems, which saw some taxpayers asked to pay too little ahead of the second payment on account deadline on 31 July 2018.

This time around, some of those who had already filed their tax return for 2017/18 ahead of the deadline at midnight on 31 January 2019 were receiving inaccurate bills from HMRC.

These excluded their payment on account, which is an advanced biannual payment made for the year ahead, with that deadline also falling on 31 January.

HMRC claimed a systems error was responsible for the latest glitch, which has since been resolved, and that the small number of taxpayers affected would not be charged extra interest or penalties.

But fears remain that further payment reminders may be inaccurate and interest may be charged on late payments.

If you're completing self-assessment this month, check the amount of tax you owe - either with us before the 31 January 2019 deadline, or double-check if you're filing your own tax return.

Who needs to submit a tax return?

The self-assessment deadline applies to around 12 million taxpayers in the UK, usually those with more than one source of income and the self-employed.

If you worked for yourself at any time in 2017/18 and earned more than £1,000 outside of PAYE, you will need to declare this by submitting a tax return online before midnight on 31 January 2019.

Payments on account

When you complete self-assessment, you can pay the tax owed to the Revenue in two instalments: on 31 January and 31 July. These are called payments on account.

In addition to midnight on 31 January 2019 being the deadline to file your tax return, it is also the deadline to make your first payment on account towards the 2018/19 tax year.

Some taxpayers may also need to make a balancing payment by 31 January 2019 to settle any outstanding debt owed to HMRC for 2017/18.

For example, let's say you owe the Revenue £6,000 from 2017/18 and you made two payments on account of £1,800 - on 31 January 2018 and 31 July 2018 - which equated to £3,600 in total.

In this case, the remaining balance of £2,400 relating to 2017/18 would need to be paid by midnight on 31 January 2019 - the same time as the first payment on account for 2018/19 is due.

What counts as a reasonable excuse?

If you're one of the 5.5 million taxpayers leaving your self-assessment to the last minute, it may be worth checking you have a valid excuse for late submission.

The Revenue classifies a reasonable excuse as something that stopped you meeting a tax obligation that you took reasonable care to meet. These include:

  •  your partner or a close relative dying shortly before the tax return or payment deadline
  •  you had an unexpected stay in hospital which prevented you from dealing with your tax affairs
  •  you had a serious or life-threatening illness
  •  your computer or software failed just before or while you were preparing your online return
  •  a fire, flood or theft prevented you from completing your tax return
  •  postal delays that you couldn't have predicted
  •  delays related to a disability.

Talk to us about your tax return.