Reasonable Excuse and MTD Appeals: How to Challenge a Tax Penalty

No one sets out to miss a tax deadline, but life gets in the way. Serious illness, a death in the family, a computer crash, a postal strike — sometimes the reasons for a late submission or payment really are outside your control. UK tax law recognises this through the "reasonable excuse" defence, which can lead to penalties being cancelled on appeal.

Under Making Tax Digital for Income Tax, the scope for reasonable excuse appeals widens. Instead of one deadline a year, you now have quarterly updates and a final declaration — five submission opportunities each year where something can go wrong, plus separate payment deadlines. Understanding what does and does not count as reasonable excuse, and how to structure an appeal effectively, is a useful piece of practical knowledge for anyone newly in MTD.

This post covers what reasonable excuse actually means in tax law, the specific situations HMRC tends to accept, the situations it tends to reject, and the step-by-step appeal process if a penalty has been imposed. It also explains why interest is different and cannot be appealed on these grounds.

What is "reasonable excuse"?

Reasonable excuse is a defence that can cancel both late filing penalties and late payment penalties. It applies where a taxpayer would otherwise have complied with their obligation but was prevented from doing so by circumstances beyond their control.

Importantly, reasonable excuse does not apply to interest. Interest on late-paid tax accrues automatically and cannot be waived on reasonable excuse grounds. The excuse defence is for penalties only.

The concept has been around in UK tax law for decades, and there is significant case law defining where the line sits. Each case turns on its own facts, but HMRC has published guidance on the factors it typically takes into account, and the First-tier Tax Tribunal has built up a body of decisions that inform how the defence is applied.

What HMRC usually accepts

The following circumstances are generally accepted as reasonable excuse:

Serious physical or mental illness of the taxpayer. Particularly where it affects capacity to manage affairs around the deadline. Medical evidence is usually expected.
Serious illness or death of a close family member. A bereavement in the immediate family is typically accepted, especially around the time of the deadline.
Fire, flood, or theft destroying your records. A genuine loss of records can be reasonable excuse, provided you notify HMRC promptly and take reasonable steps to reconstruct what you can.
IT failures. Both your own software failing and HMRC's systems being down can count. HMRC will typically expect you to have contacted them about the problem before the deadline.
Disruption to postal service. Relevant for paper filings, less so for MTD which is entirely digital.
Delay caused by HMRC itself. If HMRC has failed to process something in time or has caused a problem that prevented your submission, this can be reasonable excuse.

In each case, the key is that the circumstances were unexpected and outside your reasonable control. A burglary the day before your deadline is one thing; a gradual software problem you knew about for months is another.

What HMRC usually rejects

The following are generally NOT reasonable excuse:

The return is too difficult to complete. Complexity is not an excuse. You are expected to seek help (from an accountant, for example) in good time.
Pressure of other work. Being busy is not an excuse — everyone has other commitments.
Lack of information. If you did not gather the information you needed in time, that is usually your problem, not HMRC's.
HMRC did not send a reminder. HMRC is not obliged to remind you of your obligations. You are responsible for knowing them.
Ignorance of the law. Not knowing a deadline existed is generally not an excuse, with very limited exceptions for genuinely novel circumstances.
Insufficiency of funds. Not having the money to pay tax is not usually reasonable excuse, unless caused by truly unforeseeable external events.
Reliance on a third party. If your accountant or agent lets you down, that is generally not reasonable excuse — unless you took reasonable care in appointing and supervising them, and the failure was genuinely unforeseeable.

The last point is worth expanding. You cannot simply blame your accountant for a missed deadline and claim reasonable excuse. HMRC and the tribunals expect you to have been reasonable in your choice of agent, to have provided them with the information they needed in good time, and to have checked that submissions were being made. If you did all that and your agent still failed, you may have a case — but it is a harder one to make than you might expect.

IT failures: a growing area

With MTD, IT failures are likely to become more prominent as a reasonable excuse ground. Both your own software issues and HMRC's systems going down can be reasonable excuse, but the key factors are:

You were trying to submit on time. You did not leave it to the last minute.
You have evidence of the problem. Screenshots, error messages, support ticket references.
You contacted HMRC. Phoned them or logged the issue with them before the deadline passed (or as soon as reasonably possible).
You submitted as soon as the problem was resolved. You did not drag your feet once things were working again.

A taxpayer who waits until 7 August evening to file a Q1 update, has a software problem, and then quietly submits three days later without explanation has a weak case. A taxpayer who tried to file a week early, documented the software problem, called HMRC, and submitted the moment the issue was fixed has a strong one.

The appeals process

If a penalty is imposed and you believe you have a reasonable excuse, the process is:

Respond to the penalty notice within 30 days. You can request an internal review by HMRC, or appeal directly to the Tribunal. Most taxpayers start with the internal review.
Set out your excuse in writing. Explain what happened, when, and why it was outside your control. Include evidence where possible — medical notes, death certificates, software error logs, correspondence with HMRC.
Await HMRC's decision. If HMRC accepts your excuse, the penalty is cancelled. If HMRC rejects it, they must write to you explaining why.
If unsatisfied, appeal to the First-tier Tax Tribunal. This is a formal appeal with its own procedures. For smaller amounts, the process is relatively streamlined and does not require legal representation, though you may choose to use one.

At the Tribunal, both sides present evidence and arguments. The Tribunal then issues a written decision. Further appeal (to the Upper Tribunal) is possible but unusual for reasonable excuse cases on smaller amounts.

Writing an effective appeal

The quality of your appeal letter or submission matters. Effective appeals typically:

State the facts clearly and chronologically. What happened, when, and in what order.
Explain why the circumstances were outside your control. Make the link between the events and your inability to comply.
Show that you acted reasonably throughout. You were trying to meet the deadline, you took sensible steps to resolve the problem, you notified HMRC as soon as you could.
Include supporting evidence. Dates, medical notes, software logs, screenshots, correspondence.
Be brief and factual, not emotional. Overly personal or aggrieved appeals tend to be less effective than measured, factual ones.

A good appeal is essentially a piece of persuasive writing built on documentary evidence. If you have an accountant, they can often help you frame it well — though they cannot turn a weak case into a strong one.

HMRC discretion

HMRC also has discretion to cancel points or penalties even outside the reasonable excuse framework. This is specifically written into the new MTD regime under Finance Bill 2026. HMRC can choose not to levy a point in individual cases, and can cancel or reset penalty points — for example, in the period before an insolvency.

You cannot directly demand discretion, but if your circumstances are unusual or sympathetic, it is worth flagging them in any appeal. HMRC may exercise discretion even where strict reasonable excuse is not made out.

The interest problem

Interest on late-paid tax is not subject to any reasonable excuse defence. It accrues automatically from the original due date, regardless of circumstances. Even where you successfully appeal a penalty, the interest continues to apply.

This is deliberate policy: interest is compensation to HMRC for the time value of money, not a sanction. There is no fault-based element to interest charges, so there is no fault-based defence available. The only way to stop interest is to pay the tax.

If a penalty is cancelled on appeal, the tax that was late still carries interest for the period it was overdue. Interest charges can add up during long appeals — so it is often worth paying any disputed tax on a "without prejudice" basis pending the outcome, to stop the interest clock running.

Frequently Asked Questions

Q: How long do I have to appeal a penalty? A: You have 30 days from the date of the penalty notice to appeal. Late appeals are possible but require HMRC to accept them and are more difficult to get right.

Q: Can I appeal a penalty without going to tribunal? A: Yes. The first step is usually to request an internal review by HMRC. Only if that fails do you need to go to the First-tier Tax Tribunal. Many appeals are settled at the review stage.

Q: What evidence do I need for a reasonable excuse appeal? A: Whatever documentation supports your account of events. Medical notes for illness. Death certificates for bereavement. Insurance claims for fire or flood. Software error logs or support tickets for IT failures. Correspondence with HMRC. The stronger the documentation, the stronger the appeal.

Q: What if I just forgot? A: Simple forgetfulness is not reasonable excuse. The standard is circumstances beyond your control, not circumstances where you were careless or inattentive.

Q: If my accountant is late filing my return, can I appeal on that basis? A: Possibly, but it is an uphill battle. You would need to show that you appointed the accountant reasonably, provided them with the information they needed in good time, and that the failure was genuinely beyond both your and your accountant's control. Simple errors or inefficiencies by the accountant generally do not excuse you.

Conclusion

Reasonable excuse is a real defence, not just a theoretical one, but it requires genuinely exceptional circumstances and solid evidence to succeed. The best approach is to avoid needing it — file on time, pay on time, keep good records, and use reliable software. But when life throws something serious in your way, know that the route to cancelling a penalty exists, follow the process methodically, and document everything as you go. The system is more generous than many taxpayers realise, but it rewards preparation and clear communication, not indignation.