How to Dispute a Tax Penalty (HMRC Step-by-Step)

An unexpected penalty notice from HMRC can come as a real shock, especially if you believe you've done nothing wrong or that the circumstances behind a missed deadline were genuinely out of your control. The good news is that HMRC penalties are not final. You have the right to challenge them, and many are successfully reduced or cancelled every year.

This step-by-step guide explains the types of HMRC penalties most commonly disputed, what makes valid grounds for appeal, how to navigate the process from start to finish, and when it's worth bringing in specialist support.

Understanding HMRC Tax Penalties

Before disputing a penalty, it helps to understand what type has been issued and why. HMRC issues penalties across several categories, and the rules, rates, and appeal process can differ between them.

The most common types include:

• Late filing penalties – issued when a tax return is submitted after the deadline. For self-assessment, a £100 fixed penalty applies immediately, with further daily and percentage-based penalties for longer delays.
• Late payment penalties – charged when tax is paid after the due date. These accrue over time and can compound significantly if left unaddressed.
• Inaccuracy penalties – applied when a return contains errors that led to an understatement of tax. The penalty level depends on whether the inaccuracy was careless, deliberate, or deliberate and concealed.
• Failure-to-notify penalties – issued when HMRC isn't told about a new tax liability within the required timeframe, for example, becoming liable for VAT or self-employment tax.

It's also worth noting that from April 2026, a new points-based penalty regime extends to Income Tax Self Assessment under Making Tax Digital. For sole traders and landlords with income above £50,000, this applies from the 2026–27 tax year. Understanding which regime applies to your penalty matters before drafting your appeal.

What Is a Reasonable Excuse?

The central concept in most HMRC penalty appeals is the "reasonable excuse". If you can show that something unexpected and genuinely outside your control prevented you from meeting your tax obligation, HMRC should cancel or reduce the penalty.

HMRC's own guidance describes a reasonable excuse as something that stopped you from meeting a tax obligation that you took reasonable care to fulfil. The excuse must also be ongoing or cease to exist within a reasonable time of the obligation becoming due.

Examples that HMRC generally accepts include:

• Serious illness, hospitalisation, or a period of incapacity affecting you or someone in your care.
• The death of a close family member, particularly around the filing or payment deadline.
• An unforeseen technical failure of HMRC's own online systems.
• A fire, flood, or theft that destroyed relevant records.
• Delays caused by a third party, such as an accountant or agent, provided you gave them the information they needed in good time.

What HMRC will not typically accept includes forgetting about the deadline, being too busy, or experiencing short-term financial difficulty. The bar is genuine, unavoidable disruption, not inconvenience.

If your penalty relates to an inaccuracy rather than late filing or payment, the relevant question shifts from reasonable excuse to whether you took reasonable care in preparing your return. The existence of a genuine error, rather than a deliberate or careless omission, can significantly reduce the penalty level even if it can't be removed entirely.

Step-by-Step: How to Dispute an HMRC Tax Penalty

Step 1: Read the Penalty Notice Carefully

Start by understanding exactly what HMRC is saying. The penalty notice should state the type of penalty, the amount, the deadline you're said to have missed, and whether you have a right of appeal. Note the date on the notice, not just when it arrived, as your appeal deadline runs from that date.

Step 2: Decide Your Grounds for Appeal

You need a clear basis on which to challenge the penalty before you write to HMRC. This might be:

• A reasonable excuse for the late filing or payment.
• A factual error in HMRC's records (for example, they believe your return was late when it was not).
• A procedural issue, such as the penalty not having been properly issued.
• A dispute over the penalty level or category, particularly for inaccuracy penalties.

Be honest with yourself at this stage. A penalty appeal that doesn't have solid grounds is unlikely to succeed, and a weak appeal can occasionally complicate matters further.

Step 3: Gather Your Evidence

Whatever grounds you're relying on, support them with documentation. If you were ill, a letter from your GP or hospital records will carry weight. If HMRC's systems failed, screenshots or reference numbers from the outage help. If a third party caused the delay, correspondence showing what you provided them and when is valuable.

The stronger your evidence, the better placed you are, whether the appeal is resolved by HMRC directly or escalates to a tribunal.

Step 4: Submit Your Appeal Within 30 Days

For most penalties, you must appeal within 30 days of the date on the penalty notice. GOV.UK's guidance on penalty appeals confirms that you can appeal online through your Government Gateway account, by post, or in some cases by phone.

For Self Assessment late filing and late payment penalties, the SA370 form is the standard route for written appeals. Your appeal should clearly state what you're disputing and why, and include copies (not originals) of any supporting evidence.

If you've missed the 30-day window, you can still request a late appeal, but you'll need to provide a separate explanation for the delay. Late appeals are accepted at HMRC's discretion and are not guaranteed.

Step 5: Wait for HMRC's Response

Once your appeal is submitted, HMRC will review it and aim to respond within 45 days, though this can take longer in practice. They may ask for further information, accept your appeal in full, partially reduce the penalty, or reject the appeal entirely.

If HMRC agrees with you, the penalty will be cancelled or amended, and you'll be notified in writing. If they don't, their letter will set out why and offer you next steps.

Step 6: Request a Statutory Review (If Your Appeal Is Rejected)

If HMRC doesn't uphold your appeal, you don't have to accept that outcome. You can request a statutory review, which means an independent HMRC officer, one with no prior involvement in your case, will look at it again. A review must normally be requested within 30 days of HMRC's rejection.

This stage costs nothing and can produce a different result, particularly where the original decision-maker applied the wrong test or overlooked relevant evidence. It's nearly always worth pursuing before going to tribunal.

Step 7: Appeal to the First-tier Tax Tribunal

If a statutory review still doesn't resolve your dispute, the final avenue is an appeal to the First-Tier Tax Tribunal. This is an entirely independent judicial body with the power to overrule HMRC and cancel a penalty in full.

The tribunal process is more formal than internal review. You'll need to submit a notice of appeal, and HMRC will file its own statement of case in response. A hearing will follow, at which both sides present their arguments. For straightforward penalty disputes, this can be a relatively accessible process. For larger or more complex cases, specialist representation is advisable.

What If the Penalty Amount Seems Disproportionate?

Even where a penalty cannot be cancelled outright, there may be grounds to challenge the level at which it's been set. Inaccuracy penalties in particular are calculated on a sliding scale, and HMRC must take into account whether you disclosed the issue voluntarily, co-operated with the investigation, and the nature and extent of any underlying error.

Getting the penalty category right, and evidencing that a lower rate applies, can make a significant financial difference. This is an area where specialist advice often pays for itself, particularly where the underlying penalty is substantial.

When to Seek Specialist Advice

Many straightforward penalty appeals, particularly for a first-time late filing on a small amount, can be handled without specialist help. But there are situations where bringing in a tax barrister early in the process genuinely changes the outcome:

• The penalty is large or relates to a serious allegation, such as a deliberate inaccuracy.
• HMRC has rejected your initial appeal and the statutory review hasn't resolved the matter.
• The penalty arises from a broader HMRC investigation where other issues are also in play.
• You're unsure whether your grounds for appeal are strong enough to withstand scrutiny.
• A tribunal hearing is on the horizon and you need someone to prepare and present your case.

Early specialist input doesn't just improve your chances of success: it ensures your appeal is framed correctly from the start, which matters if the dispute runs further than you expect.

Key Takeaways

Disputing an HMRC tax penalty is a structured, step-by-step process with clear routes available at every stage, from a direct appeal to HMRC, through statutory review, and on to the First-tier Tribunal if necessary. The most important things are to act within the 30-day deadline, build your case around clear grounds and solid evidence, and not accept an initial rejection as the end of the road.

For further guidance on HMRC's approach to penalty appeals, the Low Incomes Tax Reform Group's guidance on tax penalties and interest is a useful independent resource.

Frequently Asked Questions

What counts as a reasonable excuse for an HMRC penalty?

A reasonable excuse is something unexpected and genuinely outside your control that prevented you from meeting your tax obligation on time. HMRC accepts reasons such as serious illness, hospitalisation, the death of a close relative, or a failure of HMRC's own systems. It does not accept forgetting, being busy, or cash flow problems as excuses. The excuse must also have been in place at the time of the missed deadline, not arise later.

Can I appeal an HMRC penalty after the 30-day deadline?

Yes, in some circumstances. If you miss the 30-day appeal window, you can still submit a late appeal, but you must give HMRC a separate explanation for why you didn't appeal in time. Late appeals are accepted at HMRC's discretion. If you have a genuine reason for the delay, it's always worth making the request, but the further you are past the deadline, the harder this becomes.

What happens if HMRC rejects my penalty appeal?

If HMRC rejects your appeal, you can request a statutory review by an independent HMRC officer. If that still doesn't resolve the matter, you can appeal to the First-tier Tax Tribunal, which is entirely independent of HMRC and has the power to cancel the penalty in full. A rejection from HMRC is not the end of the process; it is simply the point at which the next stage begins.

Received a penalty you want to challenge? Whether you're at the first appeal stage or facing a tribunal, Andy Wood can advise on the strength of your grounds, the right approach, and represent you through every step of the process.

Andy Wood is a specialist Tax Barrister advising individuals and businesses across the UK on HMRC penalty appeals, tax dispute resolution, and tribunal litigation.