International Tax Advisor London: What Services Should You Expect?

If you are an American living in London, finding the right tax adviser is one of the most consequential financial decisions you will make and one of the most confusing. Some general accountants offer US tax as a side service, software platforms that file your return without ever speaking to you, and advisers who know UK tax well but have limited depth on the American side of your obligations. The market is genuinely varied, and the differences between practitioners matter enormously, especially when it comes to reliable US tax preparation services and ongoing cross-border tax support.

At Jaffe & Co, we have been providing specialist international tax advisor London services to the American expat community since 1981. Our team also delivers comprehensive US tax preparation services, helping individuals and businesses meet IRS requirements while staying compliant with both US and UK tax regulations. We know what good advice looks like and we know what it delivers. This guide explains clearly what services a qualified international tax adviser in London should provide, what questions to ask before you commit, and why the standard matters more than most people realise until something goes wrong.

The Baseline: Dual-System Expertise Is Non-Negotiable

The first and most important thing to understand is this: an international tax consultant working with American expats in London must understand both the US and UK tax systems in equal depth, not one system with a passing familiarity with the other.

This distinction matters because your US and UK tax obligations interact constantly. The Foreign Tax Credit that offsets your UK income tax against your US liability requires understanding both systems simultaneously. The treaty-based position on your pension contributions requires knowing what HMRC allows and what the IRS requires. The interaction between UK Self Assessment deadlines and IRS filing dates requires coordinating two separate compliance calendars without creating discrepancies that attract scrutiny from either authority.

A generalist accountant with a US tax page on their website is not an international tax advisor London specialist. A US-focused software service that does not understand Self Assessment is not an international tax consultant. What you need and what a qualified adviser should provide is genuine depth in both systems, from the same team, under the same roof.

Service 1: Annual US Federal Tax Return Preparation

This is the foundation. Every American living in London must file a US Form 1040 annually, reporting worldwide income regardless of whether any US tax is ultimately owed. A qualified US tax preparation services provider will:

• Prepare your complete Form 1040 including all required schedules

• Apply the Foreign Tax Credit correctly to offset UK taxes already paid

• Evaluate whether the Foreign Earned Income Exclusion or FTC produces the better outcome for your specific income profile

• File any required state returns if your prior US state of residence requires continued filing

• Ensure the return is filed on time, April 15, with an automatic extension to June 15 for overseas filers, with further extension to October 15 available on request

The return itself is the starting point, but a genuinely qualified adviser does not simply prepare what you hand them. They review your financial position, identify planning opportunities and flag anything that requires additional action before the return is finalised.

Service 2: FBAR and FATCA Compliance

Two of the most consistently missed obligations for Americans in London are FBAR (FinCEN Form 114) and FATCA (Form 8938), and they are entirely separate from your tax return.

FBAR is required when the aggregate value of your foreign financial accounts exceeds $10,000 at any point during the year. FATCA applies when your total foreign financial assets exceed $200,000 at year-end as a single filer. Both obligations apply to UK current accounts, savings accounts, ISAs, workplace pensions, SIPPs and digital banking platforms, and filing one does not satisfy the other.

A qualified us uk tax advisor firm handles both as standard, not as add-ons or afterthoughts. As experienced US tax experts in the UK, we include FBAR and FATCA review in every client engagement because missing either carries penalties that start at $10,000 per violation for non-wilful failures in 2026.

Service 3: UK Self Assessment

If you are self-employed, a landlord, or earning untaxed income above HMRC's thresholds in the UK, you have a UK Self Assessment obligation alongside your US return. A genuinely qualified international tax advisor in London handles both, ensuring that your UK income is reported correctly to HMRC, that allowable UK expenses are properly claimed, and that the timing and categorisation of income across both returns is consistent and coordinated.

The UK tax year runs 6 April to 5 April, not the US calendar year, which creates reconciliation complexity that requires dual-system expertise to handle correctly. The tax paid through Self Assessment also forms the basis of your Foreign Tax Credit calculation, making accuracy on the UK side directly relevant to your US liability.

Service 4: Treaty-Based Position Filings

The US–UK Income Tax Treaty provides meaningful relief in several areas including pension income, certain investment returns and employment income situations. But treaty benefits are never automatic. They must be actively claimed by filing the correct forms, most commonly Form 8833, a Treaty-Based Return Position Disclosure, and the position must be taken consistently across every subsequent return.

An international tax consultant with genuine treaty experience will identify which positions apply to your situation, document them correctly, and ensure they are maintained properly year after year. A practitioner who overlooks treaty opportunities or takes treaty positions without proper documentation creates both missed savings and potential compliance risk simultaneously.

Service 5: Pension and Investment Reporting

UK pensions, including workplace defined contribution schemes, SIPPs and the UK State Pension, all carry US reporting implications. Depending on the structure, a UK pension may require treaty-based elections via Form 8833, potential foreign trust reporting via Form 3520 and 3520-A, or specific treatment of employer contributions as taxable compensation.

UK investments, particularly ISAs and unit trusts, may trigger PFIC (Passive Foreign Investment Company) rules, requiring Form 8621 reporting and potentially carrying punitive tax consequences if not handled correctly. A qualified US tax preparation services provider reviews your full investment and pension portfolio as part of the annual engagement, not just the income you remember to mention.

Service 6: Back-Year Compliance and Remediation

Many Americans who come to Jaffe & Co for the first time have missed prior years of US returns, FBAR filings, or both, often without realising they had an obligation. A qualified us uk tax advisor firm should offer clear, structured guidance on the available remediation pathways, including:

Streamlined Foreign Offshore Procedures - for non-wilful filers, allowing three years of returns and six years of FBARs with significantly reduced or eliminated penalties.

Delinquent FBAR Submission Procedures - for those whose returns are current but whose FBARs have not been filed.

These pathways require precise execution and honest assessment of the facts, and they are only available before the IRS initiates contact. The right time to address them is always now rather than later.

What Sets Jaffe & Co Apart

At Jaffe & Co, we are not generalists who offer US tax as a secondary service. We are attorney-qualified advisers with more than 100 years of combined experience in US and UK expatriate tax, and we are ourselves US citizens and taxpayers living with the same obligations we advise on every single day.

As US tax experts in the UK with a personal understanding of what it means to file in both systems simultaneously, our advice comes from genuine lived experience, not just technical qualification. Every client engagement covers the complete picture: US federal return, FBAR, FATCA, Self Assessment where required, treaty positions and pension reporting all coordinated, all consistent and all clearly explained.