Missed UK Tax Returns: When PAYE Was Never Enough (2026)

Missed UK tax returns are common among senior Americans in London because PAYE feels complete. It is not. Payroll settles UK employment tax; it does not settle tax on US-source RSU income outside the payroll net, US brokerage dividends, interest, or share disposals. Those items sit in Self Assessment, and unfiled years compound quietly.

If you are an executive who has been taxed at source since arriving, discovering that you have missed UK tax returns stretching back several years is unsettling but rarely catastrophic. It is a compliance-catch-up exercise with a defined sequence, defined time limits, and — critically — a US dimension that must be handled in the same motion, not afterwards. At Jungle Tax we run these remediations for banking, private equity, technology and legal clients across the two systems simultaneously, because fixing the UK side in isolation is what destroys the US foreign tax credit position.

Why PAYE Felt Like the Whole Answer

The UK's Pay As You Earn system is genuinely comprehensive for what it is designed to do. Your employer operates a tax code, deducts income tax and National Insurance at each pay date, and reconciles to a P60 at year end. For a UK national with a single employment, no investments of consequence and no equity, PAYE really does discharge the entire liability. No return is required, and none is expected.

That model breaks the moment income arises from outside the payroll. An American executive relocated to London typically arrives with, and continues to accumulate, exactly the categories PAYE cannot see:

• Restricted stock units and options granted by a US parent, where the UK payroll may capture some of the vest value but not all of it — or captures it at the wrong rate.
• A US brokerage account paying dividends and interest, with US withholding applied at source and nothing reported to HMRC by the payer.
• Disposals of vested shares, ETFs and mutual fund positions held in that US account, generating UK chargeable gains with a sterling base cost the broker has never calculated.
• US retirement account distributions, deferred compensation, and occasionally a US rental property retained after the move.
• Interest on US cash and Treasury holdings, plus any partnership or S corporation flow-through from a pre-move interest.

None of that appears on a P60. None of it is withheld by a UK employer. And because the executive sees a large PAYE deduction every month and a US withholding line on every brokerage statement, the intuitive conclusion — tax is being paid, therefore tax is settled — is entirely understandable and entirely wrong.

The notification obligation nobody mentions

UK Self Assessment is not a system HMRC pushes at you. It is a system you are legally obliged to enter. Where you have a liability that PAYE has not collected, the obligation is to notify HMRC of chargeability by 5 October following the end of the tax year in which the income arose. HMRC does not need to have sent you a notice to file for the obligation to exist. That single point is the origin of most multi-year exposure we see: no notice arrived, so no return was filed, so no notice arrived the following year either.

What Actually Triggers a Self Assessment Obligation for a PAYE Executive?

The trigger list has shifted in recent years, and some widely circulated advice is now out of date. The old rule that any PAYE taxpayer earning above £100,000 automatically had to file was raised to £150,000 and then, for 2024-25 onwards, the income-level trigger for PAYE-only taxpayers was removed altogether. Income alone no longer puts you in Self Assessment. Untaxed income does.

For a senior American in London, the practical triggers are:

• Foreign income of any material amount — US dividends, interest, distributions and pensions. These require the foreign pages (SA106) and, where UK residence applies to worldwide income, must be reported gross with credit claimed for US tax suffered.
• Capital gains — where total chargeable gains exceed the annual exempt amount, or where total disposal proceeds exceed the reporting threshold even if the net result is a loss. The reporting threshold catches far more people than the gains threshold, because a single rebalancing of a US portfolio can produce very large gross proceeds.
• Employment-related securities income not fully collected through PAYE — the classic RSU shortfall, discussed below.
• Untaxed UK income — rental income, consultancy fees, non-executive director fees paid gross.
• Claims that can only be made on a return — foreign tax credit relief, double taxation treaty relief, loss claims, and (for those eligible) claims under the foreign income and gains regime.

The RSU Problem: Payroll Withholding Is Not the Same as Correct Tax

Equity compensation is the single largest driver of missed UK tax returns in this population, and it fails in two distinct places.

The vest: withholding at the wrong rate, or on the wrong slice

When RSUs granted by a US parent vest for a UK-resident employee, the value at vest is UK employment income and should pass through UK payroll. In practice, three things go wrong. First, many US stock plan administrators default to a flat withholding rate that does not reflect the UK's additional rate plus National Insurance, leaving a shortfall the employee is required to make good — and, if it is not made good to the employer within 90 days of the relevant date, the unpaid amount itself becomes further taxable employment income. Second, where the vesting period straddles time worked in the US and time worked in the UK, only the UK-workday portion is UK-taxable, and the apportionment is almost never done correctly by a US plan administrator. Third, awards that vested shortly before or after the move are frequently treated as wholly one country's, when they are properly split.

Every one of those outcomes requires a Self Assessment return to correct. The additional pages for employment-related securities are not optional cleanup; they are how HMRC learns the real number.

The sale: a second, entirely separate tax event

Selling vested shares is a capital gains event with a UK base cost equal to the sterling value at vest, translated at the vest-date exchange rate. Two consequences follow that catch people repeatedly. A "sell to cover" transaction on vest day is itself a disposal, usually generating a small gain or loss that still counts towards disposal-proceeds reporting. And because base cost is fixed in sterling while the shares are held in dollars, a position that is flat in dollar terms can produce a substantial sterling gain purely through currency movement. UK share identification rules — same day, then the following 30 days, then the section 104 pool — must be applied to a holding the US broker reports on an entirely different basis.

US Brokerage Income: What HMRC Already Knows

A recurring assumption is that a US account is invisible to HMRC. It is not. Information flows in both directions under intergovernmental arrangements, and HMRC receives substantial data on UK-resident account holders from overseas institutions. In practice, the risk of a "quiet" unfiled position is materially higher than it was a decade ago, and the reputational and penalty consequences of being prompted by HMRC rather than coming forward voluntarily are significant.

Two structural points deserve emphasis for wealthy readers:

• US mutual funds and many US-listed ETFs are non-reporting funds for UK purposes. Gains on disposal are taxed as offshore income gains at income tax rates rather than capital gains rates, with no annual exempt amount. An executive who has held a large US mutual fund portfolio through several years of unfiled returns may have a materially worse UK position than they assume — and this is precisely the kind of item that is invisible until someone reconstructs the years properly.
• US dividend withholding is not automatically the treaty rate. Without a valid W-8BEN on file, withholding may exceed the treaty rate, and only the treaty rate is creditable for UK purposes. The excess must be reclaimed from the IRS, not credited against UK tax.

How Far Back Can HMRC Go?

Time limits determine the scope of any catch-up. They are behaviour-based, not calendar-based, which is why the characterisation of the failure matters more than its duration.

Behaviour	HMRC assessment window	Typical application
Innocent error / reasonable care taken	4 years from the end of the tax year	Genuine misunderstanding of the PAYE/Self Assessment boundary
Careless	6 years	No advice sought despite obvious foreign income
Offshore matter (non-deliberate)	12 years	Undeclared US-source income and gains
Deliberate	20 years	Conscious decision not to report

The 12-year offshore window is the one that reshapes these cases. A US executive with unreported US dividends is, by definition, dealing with an offshore matter from HMRC's perspective, so the comfortable assumption that "only the last four years are open" is usually wrong. Conversely, the deliberate 20-year window is rarely in play for someone who simply believed PAYE was sufficient — and establishing that clearly, at the outset, is a large part of the professional work.

What Are the Penalties for Missed UK Tax Returns?

There are four separate charges, and they stack.

• Failure to notify chargeability. A behaviour-based penalty calculated as a percentage of the potential lost revenue. For a non-deliberate failure disclosed unprompted more than 12 months after the tax was due, the penalty range starts above zero; disclosed unprompted within 12 months, it can be reduced to nil. This is the strongest single argument for moving quickly.
• Late filing penalties. Once HMRC issues a notice to file and the deadline passes: an initial £100, then daily penalties of £10 per day up to £900 after three months, a further 5% of the tax due or £300 (whichever is greater) at six months, and the same again at twelve months. Per return, per year. See HMRC's published penalty schedule.
• Late payment penalties. 5% of the tax unpaid at 30 days, six months and twelve months.
• Interest. Charged from the original due date. HMRC's late payment interest rate was increased from 6 April 2025 to the Bank of England base rate plus four percentage points, which makes delay materially more expensive than it was in earlier catch-up cases.

Does US-source income attract the higher offshore penalties?

This is where a good adviser saves real money. Offshore penalties are uplifted by territory category: Category 1 territories, which exchange information automatically with the UK, attract standard penalty rates, while Category 2 and Category 3 territories attract 1.5x and 2x uplifts respectively. The United States is treated as a Category 1 territory. The practical consequence is that an American executive with unreported US-source income generally faces standard-rate penalties rather than the punitive uplifts associated with genuinely opaque jurisdictions — a point that should be made explicitly in the disclosure narrative, not assumed.

US vs UK: The Same Income, Two Different Machines

Item	United Kingdom (HMRC)	United States (IRS)
Tax year	6 April to 5 April	1 January to 31 December
Filing deadline	31 January online, following the tax year end	15 April, with automatic and elective extensions for those abroad
Employment tax collection	PAYE at source; return only if income falls outside it	Withholding plus a mandatory annual return for every citizen
RSU vest	Employment income at vest, UK-workday apportioned	Ordinary income at vest, worldwide
Share disposal	Capital gain vs sterling base cost at vest; 18% / 24% rates	Capital gain vs USD basis; short or long-term rates
US mutual funds / ETFs	Usually non-reporting: offshore income gain at income rates	Ordinary capital gains treatment
Back-year correction route	Voluntary disclosure or late returns for the open years	Amended returns, or streamlined procedures where eligible
Normal look-back	4 / 6 / 12 / 20 years by behaviour	3 years generally; 6 for substantial omissions; unlimited if unfiled

How to Bring Missed UK Tax Returns Back Into Line

Step 1 — Establish the true residence and scope position first

Before a single figure is compiled, fix the residence status for every year under the Statutory Residence Test, and determine whether any year qualifies for split-year treatment or, from 6 April 2025, for the four-year foreign income and gains regime that replaced the remittance basis for new arrivals. Scope drives everything. Filing returns on the wrong scope assumption is worse than not filing at all, because it converts an innocent omission into a positively incorrect statement.

Step 2 — Reconstruct the data, not just the totals

You will need: US brokerage 1099s and full transaction histories for every open year, stock plan vest and release confirmations, grant agreements showing vesting periods, P60s and P11Ds, US federal and state returns as filed, and evidence of US tax actually paid (not merely withheld). Every dollar figure must be converted using an acceptable exchange rate basis applied consistently across all years.

Step 3 — Choose the right disclosure route

Where the exposure involves offshore matters — which US-source income is — the appropriate route is usually HMRC's Digital Disclosure Service, specifically the Worldwide Disclosure Facility. You notify HMRC, receive a disclosure reference number, and then have 90 days to submit a complete disclosure with tax, interest and a self-assessed penalty. An extension to 180 days can be requested for complex cases before the original window expires. Where the position is genuinely simple and within the ordinary window, filing the outstanding returns directly may be cleaner. That decision should never be made casually: the route chosen shapes the penalty position.

Step 4 — Register and obtain the mechanics

If you have never been in Self Assessment, you must register to obtain a Unique Taxpayer Reference. HMRC's guidance on who must send a tax return sets out the baseline. Online filing is generally limited to recent years; older years typically require paper returns or submission through the disclosure facility, which is one reason the two routes are not interchangeable.

Step 5 — Compute each year on its own terms

Each tax year must be computed with the rates, allowances and rules in force for that year — not current ones. Capital gains rates changed during 2024-25. The dividend allowance has been reduced repeatedly. The annual exempt amount has fallen sharply. A catch-up computed on today's numbers will be wrong in every prior year.

Step 6 — Build the penalty narrative

Penalty mitigation is earned through telling, helping and giving access. A disclosure that explains clearly why a sophisticated person reasonably believed PAYE was sufficient — supported by employer communications, payroll documentation and the absence of any notice to file — routinely achieves materially better outcomes than a bare set of numbers.

Step 7 — Rework the US side in the same exercise

This is the step generalist UK firms omit, and it is where most of the money is.

Protecting the US Credit Position While You Fix the UK Side

Paying additional UK tax for 2019 through 2024 does not simply cost money — it changes the correct US tax for those same years, because the foreign tax credit is what stops the same income being taxed twice.

Three mechanisms matter:

• Foreign tax credit recomputation. Additional UK tax paid on income the IRS also taxed generally creates additional creditable foreign tax on Form 1116. Because the credit is computed by income category, the UK tax must be allocated to the correct basket — general category for employment and RSU income, passive category for dividends, interest and most gains. Misallocation is the most common error, and it wastes credit.
• Treaty re-sourcing. US-source income such as US dividends and US-company RSU income creates a structural problem: a US citizen cannot ordinarily credit foreign tax against US tax on US-source income. The US-UK treaty's re-sourcing provisions in Article 24 allow certain US-source income taxed by the UK by reason of residence to be treated as foreign-source for credit purposes, within limits. Applying re-sourcing correctly is frequently the difference between full relief and genuine double taxation on exactly the RSU and dividend income at issue here.
• The foreign tax redetermination rules and the extended claim window. When foreign tax paid changes after a US return is filed, the taxpayer is required to notify the IRS of the redetermination, and Form 1116 Schedule C exists for this purpose. Separately, the statute for claiming or adjusting a refund attributable to foreign taxes runs for ten years from the due date of the return for the year the taxes were paid or accrued — far longer than the ordinary three-year refund window. In practice this means a UK catch-up covering older years can still unlock US refunds or restore credits that would otherwise have expired.

Unused credits carry back one year and forward ten. Sequencing the UK payments and the US amendments so that credits land in years with capacity — rather than in years already sheltered — is the technical work that determines whether a remediation costs six figures or is broadly cash-neutral. Our cross-border tax specialists model this before any UK return is submitted, because once filed and paid, the sequencing options narrow.

What if the US returns are also incomplete?

Frequently they are. An executive who missed UK Self Assessment has often also missed FBAR filings for UK bank and brokerage accounts, Form 8938, or reporting on a UK pension. Where the failure was non-wilful, the IRS streamlined filing procedures can resolve the US side with the miscellaneous offshore penalty reduced or eliminated for those meeting the non-residency test. Running the UK disclosure and the US streamlined submission on a coordinated timetable — with consistent figures, consistent exchange rates and consistent narratives — is essential. Inconsistent stories told to two revenue authorities that exchange information is the worst possible outcome.

The 2025-26 Changes That Alter the Analysis

• The remittance basis was abolished from 6 April 2025 and replaced with a four-year foreign income and gains regime for individuals arriving after a sufficient period of non-residence. For recently arrived Americans, this can dramatically reduce the exposure in the earliest years — but only if claimed on a return, which is impossible if no return is filed.
• Overseas Workday Relief was reformed and is now available for four years, subject to an annual cap. For executives with genuine US workdays, this is directly relevant to the RSU apportionment described above.
• The section 690 process changed from 6 April 2025 to an employer notification basis, altering how PAYE is operated on internationally mobile employees going forward.
• Late payment interest increased from 6 April 2025 to base rate plus four percentage points.
• Making Tax Digital for Income Tax began phasing in from April 2026 for those with qualifying self-employment or property income above the entry threshold — relevant to any executive with a UK or overseas rental property.

Mistakes We See Most Often

• Filing the UK years first and only then discovering the US credit position cannot be repaired for the earliest years.
• Using the US brokerage's cost basis as the UK base cost, ignoring the vest-date sterling translation.
• Treating a full US-taxed RSU vest as fully UK-taxable, or vice versa, without workday apportionment.
• Assuming US mutual fund gains attract UK capital gains rates.
• Making an unprompted disclosure without first establishing residence and scope, then having to correct the disclosure.
• Accepting an offshore penalty uplift that does not apply on the correct territory categorisation.
• Ignoring the possibility of a UK refund: in some years, correctly claimed credit relief and apportionment produce a repayment, not a liability.

Bringing It Together

Missed UK tax returns in this profile are almost never the product of avoidance. They are the product of a payroll system that did its job well enough to be mistaken for the whole system. The exposure is real, the time limits are longer than most people expect, and the penalties stack — but the position is fully remediable, and remediated properly it very often costs less than clients fear, because the credit relief that was never claimed is claimed for the first time.

What matters is sequence and coordination. One team, both jurisdictions, one set of numbers. If you have unfiled UK years behind a PAYE position, contact our cross-border team for a confidential, privileged-in-substance review. We will scope the open years, quantify the likely UK and US outcome before anything is submitted, and manage the disclosure and the US amendments as a single project. You can also review our wider US-UK tax services and private client work for context on how we handle complex, multi-year remediations for senior executives and their families.