Can AI Draft an HMRC Penalty Appeal? Reasonable Excuse, Checked

Yes, AI can draft an HMRC penalty appeal letter, but only from facts the client has given you, and an accountant must check the dates, the excuse, the evidence and the tone before it goes out. The model structures the letter well. It cannot know what happened, and it will invent a convincing reason if you leave a gap.

That last point is the whole risk. A penalty appeal rests on a reasonable excuse, which is a question of fact about one client in one week. A letter that sounds right but states an unsupported date or an excuse the client never mentioned can sink the appeal and embarrass the practice. What follows is the drafting method, the facts to collect first, and the pre-send checks that templates leave out.

Follow me on Instagram@sagnikteaches

Start with what HMRC says counts, not with the prompt

GOV.UK describes a reasonable excuse as something that stopped the person meeting a tax obligation for a valid reason. Its reasonable excuses page gives examples that include the death of a close relative shortly before a deadline, an unexpected stay in hospital, serious or life-threatening illness, computer or software failure while preparing an online return, problems with HMRC's own online services, fire, flood or theft, postal delays that could not have been predicted, delays linked to disability or mental illness, being unaware of or misunderstanding a legal obligation, and relying on someone else to send the return when they did not.

Connect on LinkedInSagnik Bhattacharya

The same page lists what will not be accepted: a cheque bounced or payment failed for lack of money, finding HMRC's online system too difficult, not receiving a reminder, and making a mistake on the return. It adds that you must send the return or payment as soon as you are able. Read that as a two-part test. The excuse has to explain the lateness, and the filing or payment has to follow promptly once the excuse ends.

Subscribe on YouTube@sagnikteaches

Hold the draft to that list. If the client's story fits the "will not count" column, no wording rescues it, and the honest advice may be to pay the penalty or to look at a different argument, such as an error in how the penalty was calculated. An AI draft should never be used to dress up an excuse that HMRC has said it will not accept.

The facts the client must give before any drafting

Templates ask for a name and a reason. Reasonable-excuse appeals turn on a timeline, so collect it first. A short intake form works:

1. The penalty. Type (late filing, late payment, inaccurate return, records), the tax, the period, the amount, the date on the notice.
2. The obligation. What was due and when: the filing deadline or payment date.
3. The excuse in one sentence. In the client's words, not the practice's.
4. The timeline. When the problem began, how it stopped them filing or paying, when it ended, and the date they finally filed or paid.
5. Why not sooner. What they did between the problem ending and filing.
6. The evidence. Documents that exist: hospital letter, funeral notice, software error screenshots with dates, emailed requests to a third party.
7. Prior history. Earlier late filings or penalties on the same account.

Keep the intake in the client's voice and date every answer. The model will turn it into a letter. You will then compare the letter to the intake line by line.

A late return after a hospital stay, dated and costed

Say a sole-trader client, a plumber, filed the 2024 to 2025 Self Assessment return online on 18 April 2026, after the 31 January deadline. GOV.UK's penalty page lists a £100 initial late-filing penalty, then daily penalties of £10 a day after three months (up to £900), then a further 5% of the tax due or £300, whichever is greater, at six months and again at twelve. This client's return went in about 11 weeks late, so the £100 applies and the daily penalties have not started. A penalty notice arrives dated 2 May.

The client says: "I was in hospital with a burst appendix from 20 January to 5 February, then recovering at home. I filed as soon as I could." Intake follows up. Admission and discharge dates are on the letters. The return was prepared by the practice but needed the client's final approval and the government gateway authorisation. The client had no strength to deal with paperwork until early March. Then the accountant's software was down for a week in March. The return went in on 18 April.

The draft the model produced from this intake claimed "I was incapacitated from January until the return was filed on 18 April." That is where an accountant stops. The hospital stay ended on 5 February. The remaining weeks need their own account: recovery, then the practice's software outage, which is a different type of excuse and raises a question about whether the client was relying on the agent. The accountant rewrites the letter as a dated sequence and asks two further questions of the client: when exactly were you well enough to approve the return, and did the practice request your approval before 18 April? The answers change what the letter can honestly say. If the gap from early March to 18 April cannot be explained, the letter should not claim one. It may be better to argue the hospital stay and recovery period and accept that HMRC may find the delay after that harder to excuse.

The drafting prompt, with placeholders and a sample output

Give the model the timeline, tell it what it must not do, and ask for flags. Use placeholders in place of identifiers.

Draft a letter appealing a penalty to HMRC from the taxpayer's side.
Use only the facts below. Do not add any date, event, document,
illness or reason that is not listed. If something needed for the
letter is missing, write [MISSING: what] instead.

Penalty: [type], [tax], [period], [amount], notice dated [date]
Reference: [UTR or reference]  Name: [name]

Excuse in the client's words: [one sentence]

Timeline (date: event):
[date]: [event]
[date]: [event]

Evidence enclosed: [list]
When filed or paid: [date]

Structure: (1) which penalty I am appealing; (2) the reasonable
excuse in one paragraph; (3) a dated timeline in short numbered
points; (4) what I did once the problem ended; (5) the evidence
enclosed; (6) a request that the penalty be cancelled and, if the
appeal is refused, a review. Plain, polite, factual. No legal
argument, no case citations, no flattery.

An illustrative result for the hospital-stay client reads well and contains one trap:

I am writing to appeal the £100 late filing penalty dated 2 May
for the 2024 to 2025 tax year, reference [UTR].

Reasonable excuse: I was admitted to hospital on 20 January and
discharged on 5 February, and I was recovering at home until early
March, which prevented me dealing with my tax affairs before the
31 January deadline.

Timeline
1. 20 January: admitted to hospital.
2. 5 February: discharged.
3. [MISSING: date the client was well enough to review the return]
4. 18 April: return filed.

The model has done the useful thing by flagging a missing date. It also wrote "early March", which came from the intake narrative, so check that phrase against the client's own words. And it did not explain 6 March to 18 April at all, which an HMRC officer will notice. The fix is human: get the date, get the explanation, or narrow the claim.

The accountant's pre-send checks

These are the checks a template leaves out. Run all of them every time. A clean AI draft is no reason to skip any.

Check 1: every date against a document

List each date in the letter and the document that proves it. Penalty notice date, deadline, event dates, filing date. If a date has no document and no client confirmation, take it out or mark it as the client's recollection.

Check 2: the excuse against GOV.UK

Does the stated excuse fit the "may count" list, and does it avoid the "will not count" list? Re-read the model's wording for creep: "was unaware" quietly becomes "was not informed by HMRC", and "forgot" becomes "was too unwell".

Check 3: causation

For each period of lateness, does the letter say how the excuse stopped the filing or payment? An illness that ended in February explains a February filing, not an April one. The model tends to describe the excuse and skip the link.

Check 4: "as soon as you are able"

Between the end of the excuse and the filing, is every week accounted for? State what the client did, even if small: gathered records, asked the practice to prepare the return, approved the figures.

Check 5: the evidence list

Every document named in the letter must be attached, redacted where it holds health detail that HMRC does not need, and referred to by its date. A letter that says "see enclosed hospital letter" with nothing enclosed is a common avoidable failure. Do not let the model describe a document you have not seen.

Check 6: the right penalty, tax and period

Match the letter's penalty type and amount to the notice. Late-filing, late-payment and inaccurate-return penalties follow different logic, so a letter that treats one as another loses credibility. If the amount looks wrong, consider whether the better argument is the calculation, not the excuse.

Check 7: the deadline for appealing

GOV.UK says you usually have 30 days from the date the penalty was issued to contact HMRC or appeal, and that if you miss it you need to give a reason. Diarise 30 days from the notice date on the day the notice arrives. If the deadline has passed, add a late-appeal reason, which is its own excuse question. Note a second clock on the same notice: GOV.UK's Self Assessment page says a penalty must be paid within 30 days of the date on the notice, appeal or not.

Check 8: who signs and how it goes

If you are acting as agent, confirm your authorisation covers this tax and the client. GOV.UK's guidance for a case with no appeal form is a signed letter to the HMRC office related to the return, with the name, reference number and the dates of what happened. For computer problems, include the date you tried to file or pay online and any error message. Check the notice itself for the right place and method for your type of penalty, as the process differs for direct and indirect taxes. For a Self Assessment late-filing or late-payment penalty, GOV.UK has its own route: an online appeal, or form SA370 or SA371 by post, and the service asks for the penalty date, the filing date, the payment date and the excuse, which is exactly what your intake form holds. The same guidance suggests the client consider paying the penalty while the appeal runs: if the appeal fails, interest runs on the penalty from its due date; if it succeeds, the money comes back with interest.

Check 9: tone and promises

No emotional appeals, no "I have never been late before" unless the history confirms it, no threats to complain, no statements about what HMRC "must" do. Read it as the officer would: short, factual, dated.

When the client relied on a bookkeeper who never filed

A cleaning company owner told her bookkeeper to submit a payroll-related return and later learnt that it had not gone in. The GOV.UK list includes relying on someone else to send a return when they did not. The prompt output reads, "My bookkeeper failed to file, so I have a reasonable excuse." The accountant's checks bite here. What did the owner do to make sure the filing happened? Was there an email asking for confirmation? Did she act when HMRC's reminder or the penalty arrived? "Relied on a third party" is an invitation to ask about the owner's own diligence, so the letter should describe the instruction given, the date, the response, and how quickly the owner acted on discovery. A draft that blames the bookkeeper without that detail is weak. Also check whether the bookkeeper's practice should be told, as a professional-indemnity matter.

When the online service failed on deadline day

An electrical contractor says the online service rejected his submission on the deadline day. GOV.UK lists problems with HMRC's online services as a possible excuse, and for computer problems it asks for the date you tried to file or pay and any error message. The model can draft the letter in minutes, but the proof is a screenshot, a reference number from the error, or a saved confirmation email with a time stamp. If the client has nothing, ask whether the agent software logged the attempt. Without a record, the letter should say so plainly and offer what exists, rather than describing an error the model has "remembered".

When the penalty figure itself looks wrong

Not every appeal is an excuse. A plumbing-firm client gets a late-payment penalty at 30 days for an amount that does not match the tax unpaid. GOV.UK's Self Assessment penalty page shows late payment penalties of 5% of the tax unpaid at 30 days, six months and twelve months; other taxes run different penalty rules, so confirm the regime from the notice first. Recalculate before drafting: what was unpaid at day 30? Was a payment on account misapplied? A quick sum shows how fast this narrows the question. If the client's records show £8,000 unpaid at day 30, 5% is £400. A notice for £520 implies £10,400 was outstanding, a £2,400 gap, and a gap of a round payment-on-account size usually means a payment was allocated to the wrong year or the wrong charge. If the figures are wrong, a short letter setting out the sums, with the payment dates and amounts, is better than any excuse. The model is a reasonable drafter of that letter once you give it the arithmetic. It is a poor calculator, so do the sums yourself.

Handling client data when you use an AI tool

A penalty file holds personal and sometimes health data. Strip identifiers before drafting, as in the prompt above, and re-insert them in your own document. Use a tool and plan whose terms you have read, because many consumer plans differ from business ones on training and retention. The tutorial on whether it is safe to use ChatGPT with client data covers the decision in more depth, and what to tell clients about your AI use gives wording for your engagement letter. For health evidence, ask the client for the minimum: a letter showing dates, not full records.

After the letter: reviews, tribunal and the paper trail

GOV.UK says that if HMRC does not change its decision, or you cannot reach agreement, you will be offered a review, and you can ask for one at any time after you appeal without waiting for the outcome. You can also take the appeal to the tax tribunal, though if you have already asked for a review you must wait for its result. For indirect taxes, the decision letter itself offers the review and gives 30 days to accept it or appeal to the tribunal. Put those dates in your diary system on the day the response arrives, not when the client next calls.

AI is useful again at this stage for one narrow job: a one-page summary of the case file for the client, with the dates and what happens next. Give it your own notes and ask for plain sentences. Keep a single folder per appeal holding the intake form, the final letter, the evidence, the posting or upload proof and every reply. If the case later goes to review, the file shows what the client told you and when, which protects the practice as much as the client. It also makes the next appeal faster, because the intake questions that mattered are already on record.

A review step you can time

A practice that handles penalty appeals regularly can set a standard. Aim for this sequence: five minutes for intake from the client (a form, not a phone call that gets summarised later), five for the draft, fifteen for checks 1 to 9, five for the client's read-through and sign-off. If a letter needs far more than that, the case probably needs conversation with the client, not more prompting. Record the penalty, the excuse, the evidence and the outcome. After a dozen cases you will know which excuses succeed in practice, and you can put that knowledge into the intake form rather than leaving it to the model.

Keep the AI step narrow. Let it order and word the client's facts, produce the evidence list and suggest follow-up questions. Keep for yourself the judgement that matters: whether the facts amount to a reasonable excuse, whether to appeal at all, and whether the draft is true. If your practice already uses AI for research notes and client letters, the tutorial on seven AI mistakes that put client trust at risk is a useful companion to this checklist. Where the ground gets technical, ask your own professional body or a tax specialist, since this tutorial describes a drafting method, not advice on any one case.

Questions practices ask about AI-drafted penalty appeals

Can I paste the HMRC penalty notice into a chatbot?

Strip the name, address, unique taxpayer reference and any account numbers first, and use placeholders. Check your engagement letter and the tool's data terms before putting any client document into it. The facts the model needs are dates, the penalty type and the excuse, not identifiers.

Does AI know what HMRC accepts as a reasonable excuse?

It knows the general idea, but it can state HMRC's current position wrongly or too confidently. Check the excuse against the GOV.UK reasonable excuse page yourself, and never let the model decide that an excuse exists. Only the client's facts can do that.

What if the 30-day appeal window has passed?

GOV.UK says that if you miss the deadline you need to give a reason for the delay. The late-appeal reason is a second reasonable-excuse question, so the letter must cover both: why the return or payment was late, and why the appeal is late.

Should the letter be sent from the client or from the practice?

That depends on your authorisation with HMRC and what the client has agreed. If you write as the agent, confirm you are authorised for that tax and that client's name and reference appear exactly as HMRC holds them. Otherwise draft it for the client to sign.

Further reads

• AI Engagement Letters for Accountants: Faster Drafts, Clear Scope — Put AI use and scope into the engagement letter.
• Best AI Tools for Chartered Accountants: Seven for a Small Practice — Seven tools for a small practice, with limits.
• How Accountants Use AI to Explain Tax to Clients in Plain English — Explain tax to clients without losing accuracy.
• AI for UK Tax Advisers: Research Notes, Client Letters and Checks — Research notes and client letters with checks.
• How Accountants Use AI to Spot Errors in Client Books — Spot errors in client books before they become penalties.
• AI Tools and AI Development: The Complete 2026 Guide — the AI hub, including every tutorial in the AI-for-business series.

Sources: GOV.UK 'Disagree with a tax decision or penalty' (penalty and reasonable excuses pages), GOV.UK 'Self Assessment tax returns: penalties', GOV.UK 'Appeal a Self Assessment penalty for late filing or late payment' (all read 4 November 2026).