What a Code of Practice 8 Letter Means for an American in Britain
Code of Practice 8 is the framework HMRC's Fraud Investigation Service uses to run a civil investigation where it believes there may be a significant loss of tax but does not allege fraud. The letter arrives from the most specialised investigators HMRC employs, it usually concerns a large sum, and it rarely comes out of the blue. For a wealthy American living in London, Edinburgh or the Home Counties, it is also the start of a problem with two tax authorities, not one.
Every page currently ranking for this subject is written for a purely British reader. None of them mentions the IRS, the foreign tax credit or the Streamlined certification you may already have signed. However, a US citizen under a COP8 enquiry faces decisions that ripple straight into the Form 1040. Pay a disputed amount on account and the American credit may be frozen. Accept a penalty labelled "deliberate" and your non-wilful certification is in jeopardy. Settle the case and you trigger a mandatory US redetermination.
At TaxYork we prepare UK and US returns together for high-net-worth clients, and we handle both sides of these investigations as one piece of work. This guide explains exactly how the process runs, where the British and American rules collide, and what to do first.
Code of Practice 8 in One Paragraph
HMRC's own Code of Practice 8 publication says the Fraud Investigation Service will investigate any situation where there may be a significant loss of tax. It covers individuals, partnerships, LLPs and companies, and every tax HMRC collects. Crucially, HMRC states it will not run the case with a view to criminal prosecution. Nevertheless, it reserves the right to change approach at any point if it suspects or finds evidence of fraud.
Why the Fraud Investigation Service Runs Non-Fraud Cases
The name misleads people. HMRC's internal guidance at TTOG3415 explains that Code of Practice 8 applies to investigations worked by specialist technical teams wherever the Code of Practice 9 contractual route is not appropriate. Its primary use is tax avoidance, and it is used only occasionally for evasion. Consequently, receiving a COP8 letter tells you HMRC thinks the arrangement or position is wrong, not that you are dishonest.
When HMRC Opens a Code of Practice 8 Investigation
Specialist investigators do not open cases on small discrepancies. They look for complexity, unusual structures and meaningful sums, and wealthy internationally mobile taxpayers tick all three boxes.
The Positions That Attract Code of Practice 8 Scrutiny
In our experience, the positions that most often draw a Code of Practice 8 enquiry for American clients are residence claims, remuneration structures and cross-border entities. A split-year or non-residence claim in the year of arrival or departure is a classic trigger, because the Statutory Residence Test turns on day counts and ties HMRC can check against travel data. Similarly, bonus or carried interest routed through vehicles that sit differently in each country, and US LLCs whose British classification is contested, invite specialist attention.
Additionally, HMRC now receives an unprecedented volume of third-party data. Automatic exchange, land registry records and open-source material all feed its risk systems. The booklet itself warns that HMRC may observe and retain publicly available internet data, including news reports, Companies House filings and unprotected social media.
How the Opening Letter Works
Before contacting you, HMRC may examine your returns and ask third parties about your affairs. When it decides to proceed, it writes to you and your adviser. It will usually give reasons, although the Code of Practice 8 booklet makes clear it does not have to. It identifies the issues it intends to focus on, while warning that other issues may be added as the case develops.
Importantly, a Code of Practice 8 investigation can reach across several years and several taxes at once. It may absorb a compliance check another HMRC office started, or run alongside one on a separate aspect of the same return.
Code of Practice 8 Versus Code of Practice 9
The two codes differ fundamentally. Code of Practice 9 invites you to admit deliberate conduct in exchange for immunity from criminal prosecution under the Contractual Disclosure Facility. Code of Practice 8 offers no such facility and demands no admission. HMRC's guidance at TTOG3420 confirms that a Code 8 case can become a Code 9 case. Our separate guide to Code of Practice 9 for US filers explains why that switch is so dangerous for an American.
How a Code of Practice 8 Investigation Runs
Once opened, a COP8 case follows a recognisable rhythm of meetings, information requests and negotiation. Understanding each stage lets you control the record rather than react to it.
Co-operation Is Your Choice, but It Shapes the Outcome
The booklet states plainly that you must decide whether to co-operate. Attendance at meetings is described as an important part of co-operation, not a legal obligation. However, co-operation directly reduces penalties, and a case handled purely by correspondence runs longer and costs more. Therefore the real question is rarely whether to engage, but how carefully to prepare before you do.
Meetings, Notes and the Record You Create
HMRC makes a written record of every meeting and you may request a copy. It may ask you to sign the notes, but you do not have to. Meetings can take place at your adviser's office, your business premises, an HMRC office or your home, and your adviser may attend throughout. Notably, you are not obliged to discuss matters in front of business partners or fellow directors.
For an American, those notes carry a second life. Anything said to HMRC becomes a fixed account of your knowledge and intentions. If you later certify non-wilful conduct to the IRS, that certification must be consistent with what the British notes record. We therefore prepare both narratives together before the first meeting takes place.
Information Requests and Statutory Powers
HMRC will ask for documents and give a reasonable time to provide them. If you co-operate fully, it may never need formal powers. Otherwise it can issue information notices under Schedule 36 and approach banks directly. Our detailed guide to Schedule 36 information notices covers the penalties and appeal rights. Remember that UK legal advice privilege protects lawyers, not accountants, so written tax advice from an accountant is generally disclosable.
Payment on Account and Protective Assessments
HMRC will ask you to make a payment on account of the tax it believes is due. Paying stops late payment interest accruing, currently charged at 7.75% according to the HMRC interest rates table. Additionally, HMRC may raise assessments before the investigation ends if it fears non-payment or if a statutory time limit is about to expire. That second point matters enormously for the US side, as we explain below.
Penalties, Time Limits and Publication Under Code of Practice 8
A Code of Practice 8 settlement normally covers tax, interest and penalties together. Each element behaves differently, and each has a different American consequence.
How Inaccuracy Penalties Are Calculated
Penalties for inaccurate returns sit in Schedule 24 to the Finance Act 2007, and HMRC's factsheet CC/FS7a on inaccuracy penalties summarises them. Careless errors attract up to 30% of the potential lost revenue. Deliberate errors attract up to 70%, and deliberate and concealed errors up to 100%. Reductions follow the quality of your disclosure: telling, helping and giving access.
Under Code of Practice 8, the disclosure is almost always prompted, because HMRC opened the case. Consequently the minimum careless penalty is 15% rather than nil, and timing your co-operation well is worth real money.
The 200% Myth for American Accounts
Many British firms warn that COP8 penalties can reach 200%. That figure comes from the offshore penalty regime, where penalties load according to the territory involved. However, HMRC's offshore penalty categories at CH403145 cap Category 1 territories at 100%, and the territory list at CH112400 places the United States in Category 1. Therefore an inaccuracy involving a New York brokerage account or US rental income is capped at the domestic scale, not 200%.
How Far Back HMRC Can Go
The ordinary window is four years, extending to six for careless behaviour and twenty for deliberate behaviour. For offshore matters, section 36A of the Taxes Management Act 1970 allows twelve years even without carelessness. Nevertheless, section 36A(7) switches that extension off where HMRC received information from another tax authority in time to assess within the normal limit. For Americans, whose accounts generate a rich trail of exchanged data, that exclusion is a live defence many advisers never raise.
Publication and Serious Defaulter Monitoring
Where penalties relate to deliberate behaviour and the sums are large, HMRC can publish your name. Its factsheet CC/FS13 on publishing deliberate defaulters warns that offshore defaults may be published unless the disclosure was unprompted. HMRC can also enrol you in its Managing Serious Defaulters programme. Our guide to the new deliberate defaulter naming threshold covers the reforms taking effect from November 2026.
Where Code of Practice 8 Collides With Your US Tax Return
This is the part no British guide covers. A Code of Practice 8 case changes your UK liability, and every change to UK tax has a direct, mandatory consequence on your American return.
Contested Tax Is Not Creditable Until the Contest Ends
US regulations treat a foreign tax you are contesting as not yet a reasonable approximation of your final liability. The contested amount is therefore not creditable until the dispute is resolved, even where you have already paid it on account. A provisional credit election exists for cash-basis taxpayers who remit contested tax, but it requires specific elections and an annual notice every year until the contest ends.
Your method also matters. An accrual-method taxpayer's settled tax relates back to the year of the income, whereas a cash-method taxpayer generally claims it in the year of payment, where there may be little US tax on foreign income to absorb it. Separately, the payment decision inverts standard British advice. UK advisers commonly recommend postponing disputed tax under appeal. For an American, postponing means nothing is remitted, no provisional credit is available and HMRC interest keeps running. Paying on account and making the election can be the better route, and the decision should be modelled rather than assumed.
Settlement Triggers a Mandatory Redetermination
When a Code of Practice 8 case settles and your UK tax increases, that is a foreign tax redetermination under section 905(c). You must notify the IRS through an amended return with a revised Form 1116, including Schedule C, whether or not your US tax actually changes. Moreover, the IRS guidance on the foreign tax credit confirms a special ten-year period for credit claims, so years you assumed were closed reopen.
In practice, many clients paid full US tax on the income HMRC is now pursuing, precisely because they believed no UK tax was due. A settlement can therefore unlock a substantial US refund, and our US tax return preparation service handles those amendments as part of closing the British case.
Penalties and Interest Earn No Credit at All
Only foreign income tax is creditable. UK penalties and late payment interest are not taxes, so they generate no US credit and no deduction for an individual. Consequently the true cost of a COP8 settlement is the penalty and interest in full, plus any UK tax that exceeds the US tax on the same income. Negotiating the penalty percentage down is worth more to an American than to a British taxpayer, because nothing on the US side softens it.
Treaty Positions and Exchange of Information
Where the investigation challenges a residence tie-breaker or another treaty position, the mutual agreement procedure in the US-UK double taxation convention may offer a route to relief from double taxation. Our tax treaty optimisation team assesses whether competent authority assistance is worth pursuing. Equally, remember that the treaty's exchange of information article allows HMRC to request information from the IRS about your American affairs.
Code of Practice 8 and IRS Streamlined Filing
Many American clients have used, or plan to use, the IRS Streamlined Foreign Offshore Procedures to fix missed US returns and FBARs. A Code of Practice 8 case does not automatically close that door, but it narrows it.
Why COP8 Is Compatible With a Non-Wilful Certification
The IRS Streamlined Filing Compliance Procedures require you to certify that your failures resulted from non-wilful conduct. Because Code of Practice 8 alleges no fraud and demands no admission of deliberate behaviour, a COP8 case can coexist with a truthful non-wilful certification. That is the key contrast with Code of Practice 9, where the admission of deliberate conduct makes Streamlined certification incompatible.
The Deliberate Penalty Label Is the Danger
However, HMRC can still categorise behaviour as deliberate within a COP8 settlement, because the penalty regime is separate from the choice of code. If you accept a deliberate penalty on the same facts you describe as non-wilful to the IRS, the two positions contradict each other. In that situation the appropriate American route is usually the IRS Voluntary Disclosure Practice, not Streamlined. Therefore never agree a behaviour category with HMRC before your US strategy is settled.
The Certificate of Full Disclosure
At the end of a case HMRC may ask you to sign a Certificate of Full Disclosure confirming that everything taxable has now been declared. The booklet warns that signing a certificate you know to be false can lead to criminal investigation. For an American, that certificate should reconcile with your FBAR and FATCA reporting, your Form 8938 and the FinCEN foreign account filings for the same years. Where US returns are also outstanding, our IRS Streamlined Filing team aligns both disclosures before either is signed.
A Worked Case Study: A Residence Claim Under Code of Practice 8
Consider an American investment banker who relocated from London to New York part way through the 2021/22 tax year. He claimed split-year treatment and excluded a £900,000 bonus from UK tax, having paid full US tax on it at 37% on his 2021 return. Years earlier, while living in London, he had elected the accrual method for claiming foreign taxes.
The Investigation
Three years later HMRC opened a Code of Practice 8 investigation, arguing that his UK ties and workdays meant the split-year conditions were never met. HMRC's opening position assessed additional UK tax of £405,000. It also requested a payment on account, which he made to stop interest running.
The Settlement
After two meetings and a detailed analysis of his workday records, the case settled on the basis that part of the bonus related to duties performed after he left. Additional UK tax fell to £240,000. Because the error was careless and prompted, the penalty was agreed at the 15% minimum, or £36,000, and roughly £38,000 of late payment interest was added.
The American Consequences
The £240,000 of UK tax, around $324,000 at an illustrative $1.35 exchange rate, became creditable once the contest ended. Because he used the accrual method, the settled tax related back to 2021, the year of the income. His US tax on the bonus comfortably exceeded the credit, so an amended 2021 return with a revised Form 1116 recovered the full $324,000 from the IRS, plus overpayment interest. By contrast, the £36,000 penalty and £38,000 of interest produced no US benefit whatsoever.
Ultimately his net cost was the penalty and interest, not the headline £240,000. Had he agreed a deliberate behaviour category to close the case quickly, the penalty would have been far higher and his earlier Streamlined certification for unrelated account reporting would have been compromised.
Responding to a Code of Practice 8 Letter
The first thirty days shape the whole case. Act methodically rather than quickly.
Your First Steps
Firstly, do not contact HMRC informally or send explanations before taking advice. Secondly, preserve every record, including computer records, because the booklet expects you to keep them throughout. Thirdly, map the years and taxes under review against your US returns, FBARs and Form 8938 filings for the same periods, so that inconsistencies surface before HMRC finds them.
Keeping Your Ongoing Compliance Clean
HMRC treats your continuing behaviour as evidence of your willingness to engage. Therefore keep filing UK returns on time and keep paying, even while the investigation runs. The same discipline applies to US filings, because a late current-year return undermines any later claim that past failures were non-wilful.
Closing the Enquiry and Appealing
If you believe HMRC has everything it needs, you may ask it to close the enquiry. Where an enquiry into a Self Assessment return is involved, section 28A of the Taxes Management Act 1970 lets you apply to the tribunal for a closure direction. Our guide to the HMRC closure notice explains the process. If you disagree with the final decision, you have 30 days to appeal, and the gov.uk guidance on tax appeals sets out the review and tribunal routes.
How TaxYork Can Help With Code of Practice 8
We handle Code of Practice 8 investigations for Americans as a combined UK and US engagement. Specifically, we prepare you for meetings, manage information requests, test HMRC's time limits and offshore penalty loadings, and negotiate the behaviour category with the US consequences priced in.
Additionally, we make the provisional credit election where it helps, file the section 905(c) redetermination and amended returns once the case settles, and align any Streamlined or voluntary disclosure with the British record. Professional bodies such as the ICAEW Tax Faculty and the Chartered Institute of Taxation set the standards our specialists work to.
Conclusion
Code of Practice 8 is HMRC's civil route for complex, high-value cases where it suspects tax is being lost but does not allege fraud. It offers no immunity and demands no admission, and it can escalate to Code of Practice 9 if HMRC finds evidence of dishonesty. For British taxpayers it is a UK problem. For Americans it is a transatlantic one.
The contested tax is frozen for US credit purposes until the case ends, the settlement forces a mandatory IRS redetermination, and the penalty and interest earn no American relief at all. Above all, the behaviour category you agree with HMRC can decide whether your IRS Streamlined certification survives. Treat both systems as one case from the first letter.
Contact Us
If you have received a Code of Practice 8 letter, speak to a specialist before you reply. Email hello@taxyork.com, call 020 3488 8606, or book a confidential consultation with our cross-border investigations team.
Disclaimer
This article provides general information about HMRC Code of Practice 8 investigations and related US filing obligations. It does not constitute tax or legal advice and should not be relied upon in place of professional guidance tailored to your circumstances. Rules, rates and HMRC practice change, and the treatment of any case depends on its full facts. Please seek professional advice before responding to HMRC or the IRS.