Missed UK Tax Returns: Appealing an HMRC Late Filing Penalty

If HMRC has issued late filing penalties, you have 30 days from the date on the penalty notice to appeal, and you must show a reasonable excuse: something that stopped you meeting the deadline despite taking reasonable care. Being abroad, being busy, or having handed the job to an adviser is almost never enough on its own.

That last sentence is where most US-connected filers come unstuck. If you have Missed UK tax returns while living in New York, Singapore or Dubai, or while sitting in London under a US passport you barely think about, the penalty notices tend to arrive in a bundle and the instinct is to write to HMRC explaining that you were overseas and thought your accountant had it in hand. HMRC refuses that letter almost every time, and the First-tier Tribunal upholds the refusal. This guide sets out what HMRC actually accepts, the arguments that succeed more often than reasonable excuse does, and the specific sequencing question that only arises when the same facts also expose a US filing failure.

What are you actually appealing? The penalty ladder

Before you draft a word, identify which penalties you have. Under Schedule 55 of the Finance Act 2009 the Self Assessment late filing ladder runs in four stages, and each stage is a separate penalty with its own appeal:

• Day one late: a fixed £100 penalty. It applies even if you owe no tax, and even if you are due a refund.
• Three months late: daily penalties of £10 per day for up to 90 days, a further £900 maximum. These require HMRC to have issued a valid decision to charge them, and to have told you the date from which they run.
• Six months late: the greater of £300 or 5% of the tax due.
• Twelve months late: a further layer of the greater of £300 or 5% of the tax due, rising sharply where HMRC concludes the failure was deliberate, and further still where the withheld information relates to an offshore matter.

A nil-liability return filed two years late therefore carries at least £1,600 of penalties per year. Three missed years is £4,800 before a penny of tax, interest or late payment penalty. For a client with a UK rental portfolio, a UK partnership interest and five open years, the numbers reach a level where the appeal is worth doing properly rather than in a single paragraph on the online form.

Why the offshore loading matters for US-connected filers

Where the missed return relates to offshore income or assets, the tax-geared penalties can be loaded well beyond the domestic rates. HMRC's offshore penalty regime grades territories into categories reflecting the quality of information exchange, and the Failure to Correct rules that followed the Requirement to Correct deadline of 30 September 2018 carry a standard penalty of 200% of the tax for a prompted disclosure, reducible to 150% for a full and accurate one and to a minimum of 100% where the disclosure is unprompted. A US person with a US brokerage account, a 401(k) drawdown or a US LLC interest sitting behind a missed UK return is squarely inside that regime. This is why a casual appeal letter is a poor idea: it can convert an unprompted position into a prompted one and cost more than the penalty you were contesting.

What does HMRC accept as a reasonable excuse?

There is no statutory definition. HMRC's own Compliance Handbook describes a reasonable excuse as something that stops a person meeting an obligation despite them having taken reasonable care to meet it, and stresses that the test has a subjective element: it turns on the circumstances of the failure and on the experience, knowledge and attributes of the particular person. A sophisticated investor with a family office is held to a different standard from a first-time filer, and HMRC will say so.

HMRC's published examples of what may count include:

• The death of a partner or close relative shortly before the deadline.
• An unexpected hospital stay, or a serious or life-threatening illness.
• Computer or software failure while you were preparing the return.
• Failures in HMRC's own online services.
• Fire, flood or theft that prevented completion.
• Unpredictable postal delays.
• Delays connected to a disability or mental illness.
• Being unaware of, or having misunderstood, a legal obligation.
• Relying on someone else to send the return, where they did not.

HMRC's published list of what will not count is much shorter: a bounced cheque or a failed payment through insufficient funds, finding the online system too difficult, not receiving a reminder, and making a mistake on the return.

Read those two lists together and the last two entries on the "may count" list look like an open door. They are not. The full guidance at GOV.UK's reasonable excuse page and the detail in HMRC's Compliance Handbook at CH160100 both qualify them heavily, and the tribunal qualifies them further.

The two conditions that quietly kill most appeals

Two riders attach to every reasonable excuse argument, and they defeat more appeals than the excuse itself:

1. The excuse must have subsisted throughout the period of default. A three-week hospital stay in December does not explain a return still unfiled the following November. HMRC will accept the excuse and then charge everything outside the window.
2. Once the excuse ends, you must put the failure right without unreasonable delay. This is the single most common reason a genuinely sympathetic case fails. A client who was seriously ill, recovered in March and filed in October has, on HMRC's view, no excuse for the March-to-October gap. Fix the failure first, appeal second.

Is being abroad a reasonable excuse for missed UK tax returns?

Almost never, and the tribunal has said so repeatedly. In a 2024 First-tier Tribunal decision (Yaqoobi v HMRC) a non-resident taxpayer filed a 2020-21 return 375 days late and faced £1,600 of penalties. He argued that he had no reliable internet access, could not reach HMRC's online service, was affected by pandemic travel restrictions, and suffered postal delays outside his control. The tribunal rejected every limb. It noted that he had filed for the two previous years while UK resident, had declared UK rental income, and had made no enquiry at all about whether the obligation continued after he left. Ignorance of the law was not a reasonable excuse where earlier returns had been filed, and the other difficulties could have been managed with greater diligence. HMRC had validly served the notice to file at his last known address, and that was enough.

The principle to take from it is uncomfortable but clear. Leaving the UK does not suspend a filing obligation; it increases the standard of diligence expected of you. If you move abroad and keep a UK income source — a let property, a partnership share, a directorship, a UK pension in drawdown, a portfolio managed from London — HMRC expects you to have told them your new address, monitored your online account, and asked whether you still needed to file. "I was overseas" is, in HMRC's framing, a description of the circumstances in which you failed to take reasonable care, not a substitute for having taken it.

What can make an overseas argument work

Being abroad occasionally supports an appeal, but only when it is the vehicle for a different point. The versions that succeed usually look like this:

• You genuinely never received the notice to file because HMRC held a superseded address and you had notified the change through a channel HMRC accepts. This is a service argument, not an excuse argument, and it is stronger.
• You were outside the UK because of an event that would itself be a reasonable excuse — evacuating a country in crisis, caring for a dying parent overseas, a serious illness treated abroad.
• The overseas element made the information genuinely unobtainable in time: a foreign administrator, custodian or plan trustee that could not produce statements before 31 January, evidenced by correspondence showing you chased.
• You were newly within the UK system and registered and filed promptly the moment you understood the obligation. A first failure, corrected quickly and voluntarily, is materially more persuasive than a first failure discovered by HMRC.

Does relying on an accountant count as a reasonable excuse?

Usually not, and the statute says why. Schedule 55 expressly provides that where a person relies on another to do something, that reliance is not a reasonable excuse unless the person took reasonable care to avoid the failure. HMRC reads that narrowly and the tribunal reads it consistently: engaging an adviser does not transfer the obligation, it transfers the work.

To make reliance stick you have to show what you did to supervise it. In practice that means evidence that you sent complete information in good time, that you chased before the deadline rather than after it, that you had no reason to doubt the adviser's competence, and that you acted immediately once you discovered the failure. A client who emailed their records on 20 January, received no acknowledgement, and did nothing until the penalty landed in March has not taken reasonable care. A client who sent records in October, chased on 5, 12 and 20 January, was told repeatedly that the return was in hand, and filed within days of discovering it had not been submitted has a real argument — and a documentary trail to prove it.

The cross-border version of this problem is particularly common. A US-connected client frequently has a US preparer and a UK accountant who do not speak to each other. Each assumes the other has the return that touches both systems. Nobody files. That is a governance failure, not an excuse, and it is one reason we insist on a single point of accountability for clients using our US-UK tax accountants team.

The argument most filers miss: was the penalty validly charged?

Reasonable excuse is the argument everyone reaches for. It is often the weakest one available. Before you concede the penalty is properly due, test the mechanics — because a penalty that was never validly raised falls away without any need to persuade HMRC that you were blameless.

• Was a notice to file validly given? The obligation to file a Self Assessment return arises when HMRC gives you a notice under section 8 of the Taxes Management Act 1970. No valid notice, no obligation, no penalty. This is a live issue where HMRC has an old address, where notices went to a former agent, or where the taxpayer was never properly registered.
• Should the notice have been withdrawn? HMRC can withdraw a notice to file where a return was not in fact required. If you had no UK liability and no other filing trigger for a year, it is often worth asking for withdrawal rather than appealing the penalty — the penalty then has nothing to attach to.
• Were daily penalties properly decided and notified? Daily penalties require HMRC to have decided to charge them and to have told the taxpayer the date from which they run. Defects here have defeated substantial daily penalty charges at tribunal.
• Are the tax-geared penalties calculated on the right figure? The 5% layers bite on the tax outstanding at the relevant date. If foreign tax credit relief for US tax paid, or double tax treaty relief, reduces the UK liability to nil, the 5% element should be nil and only the £300 floors remain.

Special reduction: the fallback nobody asks for

Schedule 55 gives HMRC a discretion to reduce a penalty below the statutory minimum if special circumstances apply. It is deliberately not defined, HMRC applies it sparingly, and it cannot simply mean ability to pay. But it exists, and a tribunal can substitute its own decision where HMRC's consideration of it was flawed. Ask for it in the alternative, in the same letter, with reasons — a disproportionate outcome relative to a nil or trivial liability is the classic fact pattern. Very few appeal letters mention it at all.

How long do you have to appeal — and what if you are already late?

The standard window is 30 days from the date of the penalty notice. Miss it and the appeal is out of time, but not necessarily dead: HMRC has a discretion to accept a late appeal, and if it refuses, the First-tier Tribunal can give permission.

The tribunal applies a structured three-stage approach to late appeals: it establishes the length of the delay, considers the reasons for it, and then weighs all the circumstances, including the prejudice to both sides and the merits of the underlying case, with particular weight on the need for statutory time limits to be respected. Practical consequences follow:

• A delay measured in years needs a materially better explanation than one measured in weeks.
• The strength of your substantive case matters at the third stage, so a late appeal should set out the merits, not just the reason for lateness.
• Do not wait until every year is reconstructed. Appeal now, in protective terms, and supplement later.

Appeal or disclose? The fork that decides everything

This is the question generalist guides skip, and it is the one that matters most to a US-connected filer with several missed years.

An appeal says: the penalty should not stand. A disclosure says: here is everything I got wrong, please assess it and apply the lowest available penalty. They are not alternatives you can run simultaneously without thought, and choosing wrongly is expensive.

If your position is a single late return with a clean history and a genuine excuse, appeal. If your position is several years of unreported offshore income — a US brokerage account, US dividends, a Roth or 401(k) distribution, a rental in Florida, an interest in a US LLC or S-corporation — an appeal against the £100 alone is the wrong instrument. The correct route is usually a disclosure through HMRC's Digital Disclosure Service, in most offshore cases via the Worldwide Disclosure Facility. You notify HMRC, receive a disclosure reference number, and then have 90 days to gather information, calculate liabilities and submit — extendable in complex cases on application. Crucially, penalty mitigation under that route depends heavily on whether the disclosure was unprompted, which is a status you can lose the moment HMRC opens an enquiry or issues a nudge letter.

The practical rule we apply: establish the full scope of the exposure before you correspond with HMRC at all. An appeal letter that volunteers "I have other years and other overseas accounts to sort out" is a prompted disclosure in everything but name.

The US side of the same facts

A US citizen or green card holder who missed UK returns has usually missed something in the US as well, because the two systems are triggered by different things and neither waits for the other. The UK charges by residence and by source; the US charges by citizenship, wherever you live. The result is that one set of facts produces two independent defaults, two independent penalty regimes and two independent relief routes — which must tell the same story.

Issue	UK / HMRC	US / IRS
Concept	Reasonable excuse (statutory, undefined; subjective element)	Reasonable cause and good faith (facts-and-circumstances)
Being abroad	Rarely accepted; raises the diligence expected of you	Not an excuse; US filing follows citizenship, not residence
Relying on an adviser	Excluded by statute unless you took reasonable care to avoid the failure	Reliance on a professional is not, by itself, reasonable cause
Automatic first-time relief	None; each penalty appealed on its facts, though special reduction exists	First Time Abate available for certain penalties with a clean compliance history
Bulk catch-up route	Digital Disclosure Service / Worldwide Disclosure Facility	Streamlined Foreign Offshore Procedures for non-willful failures
Deadline to challenge	30 days from the penalty notice; late appeals at discretion	Varies by penalty; abatement request or CP notice response window
Offshore loading	Yes — offshore penalties and Failure to Correct up to 200% of tax	Information return penalties (FBAR, 8938, 5471) can dwarf the tax

Two points follow that no UK-only guide will tell you.

First, consistency is not optional. HMRC and the IRS exchange account data automatically under FATCA and the Common Reporting Standard. If your HMRC appeal says you were unaware you had UK obligations, and your US streamlined certification says you were unaware you had US obligations, both documents need to be true, dated and internally consistent, because both are signed statements capable of being compared. A narrative drafted for one authority in isolation is a liability in front of the other. The IRS sets out its own approach at its reasonable cause penalty relief guidance, and its criteria are close enough to HMRC's to make inconsistency conspicuous.

Second, sequencing changes the outcome. The US non-willful certification under the Streamlined Foreign Offshore Procedures requires a full explanation of the failure. If you are also disclosing to HMRC, the two narratives should be prepared together, not months apart by separate firms. Clients coming to us with both problems are usually run through a single fact-gathering exercise and then split into parallel workstreams: the UK disclosure or appeal, and the US catch-up handled by our IRS streamlined filing team. Doing it in one pass is faster and materially cheaper than doing it twice.

How to appeal, step by step

1. File the outstanding return first. An appeal made while the return is still outstanding is weak on the "without unreasonable delay" limb and HMRC may not process it at all.
2. List every penalty notice by year, date and amount. Each penalty is separately appealable and the 30-day clocks run separately. Missing one leaves a live charge behind.
3. Choose the route. Most individual late filing and late payment penalties can be appealed through your HMRC online account; the alternative is form SA370 by post (SA371 for partnerships). HMRC's appeal guidance sets out both. Where the facts are complex or offshore, a full letter is better than a form field.
4. Set out the excuse with dates. When it began, when it ended, why it prevented filing, and what you did the moment it ended. Chronology carries the argument.
5. Run the alternative arguments in the same letter. Validity of the notice to file, defective daily penalty decisions, recalculation of the tax-geared element after treaty relief, and special reduction.
6. Attach evidence. HMRC does not require it up front but will ask, and an appeal supported at the outset resolves faster: medical letters, death certificates, correspondence with a custodian, dated emails to your adviser.
7. Consider postponing payment. You can normally ask for the penalty not to be pursued while under appeal. Interest treatment differs from the penalty itself, so ask explicitly.
8. If refused, escalate deliberately. You can accept HMRC's offer of an independent statutory review, or notify the appeal to the First-tier Tribunal, generally within 30 days of the decision. Alternative Dispute Resolution is available in suitable cases. A successful appeal results in repayment, with interest, provided nothing else is outstanding.

What changes in 2026 and beyond

The Schedule 55 ladder described above continues to apply to taxpayers who have not been brought into Making Tax Digital for Income Tax. Those with qualifying business or property income above the mandation thresholds are being phased into MTD from April 2026, and with it a points-based late submission regime: points accrue for each missed quarterly obligation and a financial penalty is triggered once a threshold is reached, with points expiring after a period of compliance. For internationally mobile landlords with UK property this is a meaningful change, because the number of filing obligations per year rises sharply and so does the number of opportunities to accrue a point while abroad. Thresholds and start dates have moved more than once; confirm your own position rather than assuming.

How Jungle Tax approaches these cases

We act for internationally mobile individuals, founders and families with exposure on both sides of the Atlantic, and the pattern is consistent: the penalty notice is the symptom, not the problem. Before drafting anything we establish the full scope — every open UK year, every US year, every unreported account, every information return — so that the appeal, the disclosure and any US catch-up tell one coherent story and no correspondence accidentally converts an unprompted position into a prompted one. Where the exposure is large or the facts are unhelpful, we scope the work under privilege considerations from the outset. You can see how this fits alongside our wider private client work, and there is further reading in our guides library.

If penalty notices have arrived, or you know the returns are outstanding and no notice has come yet, the position is almost always better handled before HMRC makes the first move. Contact our cross-border team for a confidential, no-obligation consultation. We will tell you honestly whether you have an appealable excuse, whether disclosure is the better route, and what the realistic exposure is on both sides of the Atlantic before you commit to anything.