Reasonable Excuse for Late Tax Return — What HMRC Accepts

When HMRC issues a penalty for a late Self Assessment tax return, the primary defence available to you is the “reasonable excuse” argument. If you can prove that something beyond your control genuinely prevented you from filing on time, HMRC should cancel the penalty.

But “reasonable excuse” is not a vague concept — it has a specific legal meaning, tested in tribunal cases and defined in HMRC's own internal manuals. Understanding exactly what HMRC considers reasonable (and what it does not) is the difference between a successful appeal and a rejected one.

The legal definition of reasonable excuse

UK tax law does not provide an exhaustive definition of “reasonable excuse.” Instead, paragraph 23 of Schedule 55 to the Finance Act 2009 states that a penalty does not arise if the taxpayer can show a reasonable excuse for the failure, and that the failure was remedied without unreasonable delay after the excuse ceased.

The landmark case Perrin v HMRC [2018] UKUT 156 established a structured test that HMRC and tribunals now follow. The test asks four questions:

1. What was the excuse?
2. When did it start?
3. When did it end?
4. Did the taxpayer file without unreasonable delay once the excuse ended?

A strong appeal addresses all four questions explicitly. This is what distinguishes a well-structured appeal from one that simply says “I was ill” without elaboration.

Excuses HMRC accepts

Based on HMRC's published guidance (in their internal manual CH160200 and the SA370 form guidance), the following are recognised reasonable excuses:

Serious illness or hospitalisation

This is the most commonly accepted excuse. If you were physically or mentally unable to file your return due to illness, HMRC will consider this reasonable. This includes hospital stays, surgery recovery, serious infections, and mental health crises such as severe depression or anxiety.

Supporting evidence: GP letters, hospital discharge summaries, prescription records, or a letter from a mental health professional.

Bereavement

The death of a spouse, partner, close family member, or someone you cared for is accepted as a reasonable excuse. HMRC recognises that grief, funeral arrangements, and estate administration can prevent someone from meeting filing deadlines.

Supporting evidence: death certificate, funeral director correspondence, or a brief statement explaining the relationship and impact.

Fire, flood, or natural disaster

If a fire, flood, storm, or other disaster destroyed your records, damaged your property, or forced you to evacuate, this is a strong reasonable excuse. HMRC recognises that replacing records and stabilising your situation takes time.

IT failures and software problems

If HMRC's own website crashed near the filing deadline, or if your tax software experienced a critical failure, this counts as a reasonable excuse — provided the failure was not caused by your own equipment and you attempted to file before the deadline.

This excuse is strongest when HMRC's systems had documented outages. HMRC publishes service availability data, and referencing specific dates and times strengthens your case significantly.

Postal delays

If you were filing a paper return and postal delays prevented it from arriving on time, HMRC may accept this — particularly if you can show proof of posting (such as a Royal Mail tracking receipt) that demonstrates you sent it before the deadline.

HMRC's own errors

If HMRC failed to send you a notice to file, gave you the wrong UTR number, provided incorrect guidance, or made an error in your tax records that prevented you from filing, this is a strong reasonable excuse. HMRC cannot penalise you for their own mistakes.

Reliance on a third party

If your accountant, tax agent, or bookkeeper let you down at the last minute — for example, by failing to submit your return despite being instructed to do so — this can be a reasonable excuse. However, HMRC expects you to have given them adequate time and instructions. Simply appointing an accountant late in the process is not enough.

Excuses HMRC does NOT accept

HMRC is clear about what does not constitute a reasonable excuse. The following will almost certainly result in a rejected appeal:

• “I forgot” — forgetfulness is not a reasonable excuse under any circumstances
• “I was too busy” — HMRC considers tax filing a legal obligation that must be prioritised
• “I didn't know about the deadline” — ignorance of the law is not a defence
• “I couldn't afford an accountant” — you can file your own return for free via Government Gateway
• “I didn't owe any tax” — the penalty is for late filing, not late payment; you must file even if you owe nothing
• “HMRC owe me a refund” — a refund position does not exempt you from the filing requirement

How to present your reasonable excuse

The way you present your excuse matters as much as the excuse itself. A well-structured appeal should:

• State your penalty reference number and the tax year involved
• Clearly describe what happened, with specific dates
• Explain why this prevented you from filing on time
• Show that you filed as soon as the obstacle was removed
• Reference the relevant legislation (Finance Act 2009, Schedule 55; Perrin v HMRC)
• Attach supporting evidence where available

The tone should be factual and professional. Emotional pleas or complaints about the penalty system are counterproductive. HMRC officers assess appeals against legal criteria, not sympathy.

The “acting without unreasonable delay” requirement

Even if you had a genuine reasonable excuse, HMRC also requires that you filed your return without unreasonable delay after the excuse ceased. For example, if you were in hospital until 15 February but did not file until June, HMRC may argue that the delay between your recovery and your filing date was unreasonable.

Your appeal should explicitly address this point, explaining either that you filed promptly after recovery, or that additional factors (such as ongoing recovery time or needing to reconstruct records) caused the further delay.