Introduction: When the Competent Authority Becomes Your Only Route
A competent authority request is the remedy wealthy Americans in Britain reach for when the foreign tax credit has failed. Both revenue services still want the same money. Most cross-border double taxation resolves itself through ordinary mechanics. You pay HMRC, you claim a credit, the arithmetic works. Occasionally, however, the two systems disagree about something structural, and no amount of careful return preparation can bridge the gap.
Sourcing disputes cause most of these deadlocks. HMRC treats a slice of your equity award as UK employment income, while the Internal Revenue Service treats the same slice as US-source. Consequently the credit mechanism collapses, because the United States does not grant a foreign tax credit against income it considers its own. You are left paying twice on the same pounds.
At TaxYork we see this most often with partners, managing directors and founders whose income straddles a transatlantic move. Importantly, the treaty anticipated exactly this problem. Article 26 creates a formal channel between the two tax administrations. Notably it remains available to you even though the saving clause strips most other treaty benefits from US citizens.
How a Competent Authority Case Actually Begins
The mechanism is administrative rather than judicial. You present a written case to the designated official in one country. That official then engages their opposite number under the mutual agreement procedure. Furthermore the process runs entirely separately from domestic appeals, which continue on their own timetable unless you pause them deliberately.
Neither revenue service charges a fee. Nevertheless the evidential burden sits squarely with you, and a thin submission simply produces a slow refusal. Therefore preparation determines the outcome far more than persistence does.
Who Needs This Most
High earners with equity compensation face the greatest exposure, because vesting periods routinely span both countries. Additionally, partners in transatlantic firms and owners drawing from businesses on both sides encounter characterisation disputes that the credit rules cannot absorb.
The common thread is straightforward. Sometimes double taxation arises from a disagreement between the two systems rather than from your own filing error. In that situation the ordinary remedies run out and Article 26 begins.
What the US-UK Treaty Actually Says in Article 26
Generic commentary on this subject quotes the OECD Model or the US Model Convention. Those texts differ from the agreement that actually governs you, and the differences matter enormously.
Resident or National: The Words That Matter
Article 26(1) of the 2001 US-UK Convention permits a person to present a case to the competent authority of the Contracting State of which he is a resident or national. That single word transforms the position for Americans abroad, as the next section explains. Moreover it means you are not automatically shut out simply because Britain, not America, is now your treaty home.
The provision applies "irrespective of the remedies provided by the domestic law of those States". Accordingly you need not exhaust a UK appeal or a US audit before approaching a competent authority.
The Three-Year and Six-Year Deadlines
Article 26(1) imposes a dual limit that generic guidance consistently misstates. A case must be presented within three years from the first notification of the action producing the taxation. Alternatively the deadline is "six years from the end of the taxable year or chargeable period" concerned, if that falls later.
Notably the later of the two applies. Therefore a filer who discovers the problem slowly still has the six-year window. That is more generous than the bare three-year rule most articles quote. On the UK side, section 125 of TIOPA 2010 supplies a comparable six-year domestic backstop.
Agreements Override Domestic Time Limits
Article 26(2) contains the provision that makes the whole exercise worthwhile. Any agreement the two authorities reach "shall be implemented notwithstanding any time limits or other procedural limitations" in domestic law.
In other words, a closed year can be reopened to give effect to the agreement. However, that override applies to implementing the agreement, not to your unilateral refund rights, which is precisely why protective claims matter so much.
The Saving Clause Does Not Take This Away
American readers rightly ask whether the treaty offers citizens anything at all. Article 1(4) reserves each country's right to tax its own citizens as though the treaty did not exist. That guts most articles for US persons.
Why Article 26 Survives
The saving clause carries a list of carve-outs, and Article 26 sits on it alongside Articles 24 and 25. Consequently your right to bring a competent authority case survives your citizenship in full. This point deserves emphasis, because many advisers assume the saving clause disposes of the question entirely.
Article 9(2), Article 17(1)(b), 17(3) and 17(5), and Article 18(1) and 18(5) appear on the same protected list. A separate and narrower list applies only to people who are neither citizens nor green card holders.
What the 2002 Protocol Changed
Read the carve-out list from the 2002 Protocol rather than the original convention, because the Protocol replaced Article 1(5) outright. The unamended text understates the relief available, particularly on pensions.
We cover the wider treaty position in our guide to claiming a US-UK treaty position on Form 8833. Getting the disclosure right supports any later competent authority filing.
The Residence Trap That Turns Americans Away
Here is the gap that costs people their remedy, and no competitor page addresses it.
Article 4(2) and Why You Are Not a US Resident
The IRS page on competent authority assistance states that the service is for persons who are US residents for treaty purposes. Read literally, that excludes most Americans settled in London. Article 4(2) is narrower than that. A US citizen is a resident of the United States only with a substantial presence, permanent home or habitual abode there.
Therefore an American genuinely established in Britain is a UK treaty resident, not a US one. Many filers read the IRS page, conclude the door is shut, and abandon a valid claim.
Filing as a National Instead
The treaty text resolves the difficulty. Because Article 26(1) says "resident or national", a US citizen qualifies through nationality regardless of where they live. Accordingly the IRS remains open to you, and so does HMRC as your state of residence.
You therefore hold a genuine choice of forum, which is unusual and valuable. Related residence questions arise constantly here. Our guide to proving US residency for an HMRC treaty claim explains why a certificate of residence from HMRC is usually the correct instrument.
Choosing Which Competent Authority to Approach
Strategy should drive the choice. Approach the authority you need to *move*, because that administration must be persuaded to give ground. Suppose HMRC has assessed aggressively. A UK filing under Statement of Practice 1 (2018) then puts the case before the people who can withdraw the charge.
Conversely, where the IRS position creates the conflict, file with the US competent authority. Similar tie-break mechanics apply to entities, as our note on dual-resident company treaty tie-breakers sets out. However the individual rules in HMRC's guidance on dual residents differ in important respects.
There Is No Arbitration Backstop in This Treaty
This is the most consequential correction in the article, and the leading pages on the subject get it wrong.
Endeavour Is Not a Guarantee
Article 26(2) obliges each competent authority only to "endeavour" to resolve the case. Neither the 2001 Convention nor the 2002 Protocol contains any arbitration provision whatsoever. We verified this directly against both primary texts rather than relying on commentary.
Consequently the two administrations can simply fail to agree, and you have no binding remedy when they do. Many widely-read articles describe mandatory arbitration timetables drawn from the US Model Convention, which does not govern this relationship.
Why the Multilateral Instrument Does Not Help
British readers sometimes point to HMRC material referring to mandatory binding arbitration under the Multilateral Instrument. That route is genuinely unavailable here, because the United States never signed the instrument and shows no sign of doing so.
The UK-US pair therefore sits outside the arbitration framework that covers many other British treaty partners. Accordingly your leverage is evidential, not procedural.
What This Means for Your Strategy
Since no tribunal will break a deadlock, the quality of your opening submission carries disproportionate weight. Furthermore you should preserve every domestic remedy in parallel, because a failed competent authority case leaves you with whatever rights you kept alive.
Realistic timescales reinforce the point. OECD figures for 2024 put the global average near 27 months to close a case. United States cases average around 25 months outside transfer pricing. Plan for two years, not two months.
Building a Request That Works
Both administrations publish their requirements, and both reward precision. The IRS overview of the MAP process and HMRC's introduction to MAP describe the mechanics from each side.
What HMRC Requires
Britain prescribes no form at all. You present the case in writing to the UK competent authority, following HMRC's description of the mutual agreement procedure. Supply enough information and documentation to let HMRC assess it fully. Because nothing is standardised, weak submissions are common and easily bettered.
Include the treaty article in dispute, the computation of the doubled tax, the correspondence establishing first notification, and your residence evidence. HMRC also operates a parallel route for companies objecting to incorrect taxation under a treaty.
What the IRS Requires
The American side is far more prescriptive. Revenue Procedure 2015-40 governs the content and timing of requests. Moreover it directs individual treaty matters outside transfer pricing to the Treaty Assistance and Interpretation Team, not to the pricing programme.
Pre-filing consultation is available and worth using. Additionally the revenue procedure expects you to notify the service promptly, since delay materially reduces the relief achievable.
Protective Claims: The Step That Saves the Refund
This is where cases are won or lost administratively. Filing a competent authority request does not itself stop the American refund clock. Therefore you must lodge a timely protective claim under section 6511 to keep the year open. The IRS says so explicitly in its own guidance.
Take equivalent steps in Britain. Therefore preserve your HMRC appeal rights on the same income while the competent authority case proceeds. A negotiated outcome can then be implemented on both sides.
Case Study: A Vesting Dispute That Cost $185,000
An American managing director relocated from New York to London in 2022. His equity awards had been granted while he worked in Manhattan, but they vested in 2024 after two full years of London service.
The Position We Inherited
HMRC taxed the awards as UK employment income by reference to UK workdays, charging tax at 45% on the apportioned amount. Meanwhile the IRS treated a $500,000 slice of the same vest as US-source. Its basis was that the grant-to-vest period included substantial American workdays.
The conflict was structural rather than arithmetical. His previous preparer claimed a foreign tax credit, which the sourcing position defeated. The United States allows no credit against income it treats as domestic. Consequently roughly $185,000 of US tax sat on income HMRC had already taxed in full.
The Request
We first tested treaty re-sourcing, which solves many of these cases without any formal filing. Here it fell short, because the two administrations genuinely disagreed about the workday apportionment itself rather than merely about credit placement.
We therefore filed with the US competent authority as a national, within the six-year window, supported by contemporaneous travel records, board minutes and the plan documents. Protective refund claims went in simultaneously for 2024.
The Outcome
The authorities agreed an apportionment consistent with HMRC's workday analysis after twenty-six months. The IRS accordingly re-characterised the disputed slice as foreign-source, and the credit came through. Crucially the protective claims allowed the refund despite the ordinary limitation period having run.
He recovered $185,000 plus statutory interest. Notably, had the protective claims been omitted, Article 26(2) would have permitted implementation of the agreement while his unilateral refund right had already lapsed.
How TaxYork Can Help
We prepare US and UK returns for wealthy Americans in Britain, and treaty conflict work sits naturally alongside that. Specifically, we identify whether your double taxation is a credit problem or a genuine treaty dispute. Furthermore we test re-sourcing and ordinary relief first, because a competent authority case should never be the opening move.
Where a formal request is warranted, we build the submission, file the protective claims on both sides, and manage the correspondence through to implementation. Our tax treaty optimisation service and US tax return preparation work together throughout. Where earlier years also need correcting, our IRS Streamlined Filing service addresses the compliance history in parallel, using the IRS Streamlined Filing Compliance Procedures.
Conclusion
The competent authority route is underused because it is misunderstood. Three corrections carry most of the value for Americans in Britain. Article 26 survives the saving clause, so your citizenship costs you nothing here. The treaty lets you file as a national, so the residence wording on the IRS website does not exclude you. Above all, no arbitration backstop exists in this treaty pair, which makes your evidence the only real leverage you hold.
Deadlines and protective claims decide the rest. Ultimately a competent authority case rewards filers who move early, document thoroughly and keep every parallel remedy alive. Professional bodies including the Chartered Institute of Taxation and ICAEW publish useful background, though neither substitutes for treaty-specific analysis of your own facts.
Contact Us
If both HMRC and the IRS are taxing the same income, speak to us before a deadline passes. To review whether a competent authority request fits your position, book a consultation with our cross-border team.
Email hello@taxyork.com or call 020 3488 8606. Alternatively, contact us through the website and we will respond within one working day.
Disclaimer
This article provides general information about the competent authority and mutual agreement procedure under the US-UK double taxation convention and does not constitute tax advice. Treaty outcomes depend heavily on individual facts and on legislation current at the date of publication, which may change. You should obtain professional advice before acting. TaxYork accepts no liability for action taken in reliance on this article.