Specialist US UK Tax Services: Who Is Authorised to File

Specialist US UK tax services cannot begin with a tax return. They begin with authority. Before any adviser can pull your IRS transcripts, read your HMRC record or file a single form, you must grant separate, tax-specific permissions on each side: IRS Form 2848 or 8821 in the United States, and a 64-8 or digital handshake at HMRC. Missing authority is the single most common reason a multi-year catch-up stalls.

Most people engaging a cross-border firm assume the hard part is the technical work: the streamlined certification narrative, the passive foreign investment company calculations, the treaty positions on a UK pension. In practice, the technical work is rarely what delays a case by six months. What delays it is a client who signed a beautifully drafted engagement letter and then never signed the one-page authorisation that lets the firm actually see the record it is being paid to fix.

This guide sets out the authorisation layer in full — every permission a specialist genuinely needs on both sides of the Atlantic, what each one does and does not allow, what you must still sign with your own hand, and the sequencing that keeps a US-UK compliance catch-up moving. Jungle Tax runs this sequence at the start of every engagement, before a single figure is entered.

Why authority is the first bottleneck in any US-UK catch-up

A multi-year cross-border catch-up is an evidence exercise before it is a filing exercise. To scope the work honestly, a specialist needs to establish four things: what has actually been filed in the US, what has actually been filed in the UK, what third parties have already reported about you to each authority, and whether either revenue body has already opened a compliance check.

None of those four questions can be answered from your own paperwork alone. Clients routinely misremember which years were filed, hold incomplete copies, or have used a preparer who filed something they never saw. The authoritative answers live inside IRS transcript systems and HMRC's agent-facing records — and both are gated by authorisation.

The consequence is a specific and avoidable failure mode. The firm scopes the engagement on the client's recollection, quotes on that basis, then discovers three months in that two of the "missing" years were in fact filed, that a Form 5471 obligation exists for a UK limited company nobody mentioned, or that HMRC has already issued a discovery assessment. The scope changes, the fee changes, and — far worse in a disclosure context — the voluntary character of the filing may be at risk.

Authority also protects the voluntariness of a disclosure

Both the IRS streamlined procedures and HMRC's disclosure facilities depend on you coming forward before you are approached. Transcript and record access is how a competent adviser confirms that you still qualify. Filing blind, without confirming that no examination or enquiry is open, is not a technicality — it is the difference between a penalty-free path and a very expensive one.

Who is legally allowed to file and represent you in the United States?

The US draws a sharp line between preparing a return and representing a taxpayer. Both matter for a catch-up, and they are governed by different rules.

Preparing your return: the PTIN requirement

Anyone who prepares a US federal return for compensation must hold a current Preparer Tax Identification Number and enter it on the return. A PTIN is a registration, not a credential — it certifies nothing about competence, and it does not confer any right to speak to the IRS about your case. When a firm tells you it "files US returns", the PTIN is the floor, not the qualification.

Representing you before the IRS: unlimited practice rights

Only three categories of practitioner hold unlimited rights to represent taxpayers before the IRS on any matter, for any year, before any office: attorneys, Certified Public Accountants, and Enrolled Agents. Enrolled Agents are federally licensed specifically for tax and are the credential you will most often encounter in a UK-based US tax practice. Certain other preparers hold limited rights that generally extend only to returns they personally prepared and to specific IRS functions.

This distinction becomes decisive the moment a catch-up turns contentious. If the IRS queries a streamlined submission, questions a treaty position on your UK pension, or opens an examination, only a representative with unlimited practice rights can carry the argument. A firm without a credentialed representative on the file must hand you off at exactly the point you most need continuity.

Form 2848 versus Form 8821: which one does your case need?

These two forms are routinely conflated, including by advisers. They do materially different things.

• Form 2848, Power of Attorney and Declaration of Representative. Grants a named, credentialed individual authority to represent you before the IRS for specified tax matters and specified periods — to receive notices, discuss the case, respond to examinations and, where the form so specifies, sign certain agreements. It can only name individuals, not firms, and each representative must sign the declaration attesting to their eligibility to practise. See the IRS guidance on Form 2848.
• Form 8821, Tax Information Authorization. Grants access to inspect and receive confidential tax information for the periods listed — nothing more. It confers no right to argue, negotiate or represent. Crucially, it can name a firm or entity rather than only individuals, which makes it the practical instrument for transcript access across a team. See Form 8821.

The competent sequencing in a catch-up is usually both, in order: an 8821 immediately, so the firm can pull account, return, wage-and-income and record-of-account transcripts and diagnose the true position; and a 2848 for the specific years and matters where representation may be needed. Advisers who ask only for a 2848, or only for an 8821, are usually working from a domestic template rather than a cross-border one.

Specifying years correctly — the error that costs a month

Both forms require you to identify tax matters and periods with precision. A 2848 or 8821 that names only the current year is useless for a six-year catch-up. Blanket future-year language is restricted, and the IRS will reject an authorisation that overreaches. For an offshore catch-up the authorisation typically needs to span the full delinquency window plus the years already filed, and to cover the specific form types at issue — income tax, information returns and, where relevant, FBAR examination matters.

FBAR is a separate authority: FinCEN Form 114a

This is the trap that catches even well-run domestic firms. The FBAR is filed with FinCEN through the BSA E-Filing System, not with the IRS, and a Form 2848 does not by itself authorise a third party to submit it. To have your preparer e-file the FBAR you must complete FinCEN Form 114a, the Record of Authorization to Electronically File FBARs. It is signed by you and by the filing firm, retained by both, and — unlike the IRS forms — it is not submitted to the authority; it is produced on request. Where spouses file a single joint report, both must sign the 114a. Background on the reporting obligation itself is on the IRS FBAR page.

ITINs and Certified Acceptance Agents

If a non-US spouse or dependent needs to be included on a joint return, an Individual Taxpayer Identification Number is required, and the identity documentation must be certified. A Certified Acceptance Agent is separately authorised by the IRS to certify passports and supporting documents so that you do not have to post an original passport to Austin, Texas. In a UK-based practice this is a distinct authorisation from anything discussed above, and it is worth confirming whether your firm holds it before you are asked to surrender a passport for several weeks.

What does agent authorisation actually mean at HMRC?

HMRC's architecture is different in kind. Where the US grants representation rights to an individual practitioner, the UK grants agent status to a firm — and then requires a separate authorisation per tax head, through a route that varies by tax. There is no single UK equivalent of the 2848.

The three routes: paper 64-8, online agent authorisation, and the digital handshake

• Paper form 64-8. The traditional instrument. It covers Self Assessment, PAYE for individuals, the Construction Industry Scheme and trusts, and is posted to HMRC's Central Agent Authorisation Team. It is slow, but it works for clients who cannot authenticate online — which describes a great many long-term non-residents. HMRC's client-facing guidance is at Authorising an agent to deal with your tax affairs.
• Online agent authorisation. The agent submits a request through HMRC online services; HMRC posts an activation code to the client's address of record, which the client passes to the agent within a limited window. The dependency on physical post is precisely why this route fails so often for overseas clients.
• The digital handshake. The agent generates an invitation link from the Agent Services Account; the client signs in with their own Government Gateway credentials and confirms the authorisation. The link is time-limited — commonly around 21 days — and expires unactioned. This is now the required route for several taxes.

Which route applies to which tax?

This is where generalist guides go wrong, because the answer is not uniform. Self Assessment can be authorised by paper 64-8 or online agent authorisation. Capital Gains Tax on UK property disposals — the 60-day reporting regime that catches so many departing Americans selling a London flat — is authorised by digital handshake only. The Trust Registration Service is likewise digital-handshake only. VAT sits on the newer digital service. HMRC's agent-facing guidance is at How to get authorised to act as a tax agent.

The practical implication for a cross-border client is that one signature does not cover the estate. A US citizen with UK employment income, a UK rental property, a UK company and a family trust may need four separate authorisations through three different mechanisms — and each is a separate point of failure.

Making Tax Digital for Income Tax: the 2026 authorisation change nobody flags early

With Making Tax Digital for Income Tax phasing in from April 2026 for qualifying sole trader and property income above the relevant threshold, an existing signed 64-8 does not, by itself, give an agent access to MTD obligations. Authorisations generally need to be linked to or copied across to the Agent Services Account, and in many cases a fresh digital handshake is required before quarterly submissions can be made. HMRC has actively encouraged agents to migrate authorisations early to avoid a bottleneck.

For US citizens with UK rental property this matters more than it first appears. The UK reporting rhythm shifts from one annual return to quarterly updates plus a final declaration, while the US side remains annual. Getting the authorisation architecture wrong here does not just delay a filing; it can cause missed quarterly obligations on the UK side while the US catch-up is still running. Our UK tax services team handles this migration as a standing item at onboarding.

The overseas-client trap: no UK postcode

Here is a failure mode that no generalist page documents, and that we encounter almost weekly. Several HMRC authorisation journeys validate the client against a UTR and a UK postcode. A long-term non-resident living in New York, Dubai or Singapore has no UK postcode to enter, and a foreign address is rejected as invalid. The digital route simply cannot be completed.

The workarounds are unglamorous and slow: a paper 64-8 posted to the Central Agent Authorisation Team, ensuring HMRC's address of record is correct first, and in some cases a call to establish or correct the record before the authorisation can be processed at all. Budget weeks, not days. A firm that has not planned for this on a non-resident file has not run many non-resident files.

US versus UK authorisation: a side-by-side comparison

Dimension	United States (IRS / FinCEN)	United Kingdom (HMRC)
Who holds the authority	A named individual practitioner (2848); a firm may be named on 8821	The agent firm, under its agent codes and Agent Services Account
Credential required to represent	Attorney, CPA or Enrolled Agent for unlimited practice rights	No statutory licence to act as a tax agent; professional body membership is voluntary
Information-only access	Form 8821, Tax Information Authorization	Limited authorisation options; otherwise full agent authorisation per tax
Full representation	Form 2848, Power of Attorney	Form 64-8 or digital handshake, per tax head
Scope of one signature	Specified tax matters and specified periods only	Specified taxes only; a separate route may apply per tax
Foreign account reporting	Separate authority: FinCEN Form 114a for FBAR e-filing	No direct equivalent; foreign accounts reported within Self Assessment
Typical activation time	Days to a few weeks depending on submission channel	Minutes for a digital handshake; several weeks for paper 64-8
Main failure mode for expatriates	Periods specified too narrowly; FBAR authority forgotten	No UK postcode for digital validation; posted activation codes never arrive
Does it let the agent sign the return?	No — separate e-file signature authorisation is required	No — the taxpayer's declaration remains the taxpayer's

What must you still sign personally?

Authorisation is not delegation of your signature. Even with full authority in place on both sides, several documents remain irreducibly yours. Clients who plan a long absence, a hospital stay or extended travel during a catch-up need to know which ones.

On the US side

• The streamlined certification. The non-willfulness certification used in the Streamlined Foreign Offshore Procedures must be signed by the taxpayer personally, and by both spouses where a joint submission is made, each providing their own explanation. A paid preparer signing in a professional capacity does not substitute for your signature. The IRS streamlined procedures FAQs address signature mechanics, including a limited relief route where one spouse cannot sign an amended return.
• The e-file signature authorisation. Where a return is filed electronically by your preparer, you sign an IRS e-file signature authorisation permitting transmission with your self-selected PIN. This is per return, per year — six years of catch-up means six authorisations.
• The FBAR authorisation. FinCEN Form 114a, as above, signed by you before the firm can transmit.
• The returns themselves, where paper-filed. A meaningful volume of catch-up work still goes on paper, whether because the year is too old to e-file or because a submission must be assembled as a physical package. Wet signatures and international courier time both belong in the project plan.

On the UK side

• The Self Assessment declaration. The agent submits, but the declaration that the return is correct and complete is yours. A responsible firm will require your written approval of the final figures before submission and retain it.
• Disclosure submissions. Where a UK disclosure facility is used, the offer or disclosure is made in your name and requires your confirmation of completeness.
• The digital handshake itself. Only you can complete it, using your own Government Gateway credentials. No competent agent will ever ask for those credentials — HMRC's guidance is explicit that agents should not access clients' sign-in details, and any firm that asks should be declined on the spot.

How a missing authority stalls a catch-up: a worked timeline

Consider a common profile: a US citizen who has lived in London for eleven years, has UK employment income, a workplace pension, an ISA, a small UK limited company and a jointly held current account. Six years of US returns are missing, FBARs were never filed, and the UK returns were filed by a domestic accountant who was never told about the US citizenship.

With authority handled correctly, the shape of the engagement is roughly this: Form 8821 signed and submitted in week one, transcripts pulled and the true filing history established within a fortnight; a UK authorisation initiated in parallel, with the digital handshake completed the same week if the client can authenticate; scoping finalised in week three on evidence rather than recollection; document gathering and the technical build through weeks four to twelve; certification narrative drafted, reviewed and personally signed; submission assembled and filed.

With authority handled badly, the same case looks quite different. Scoping proceeds on recollection. In month two the firm discovers that two supposedly missing years were filed, requiring amendment rather than delinquent filing, which changes the procedural route. In month three a paper 64-8 is finally posted because the client has no UK postcode, and nothing can be confirmed on the UK side until it is processed. In month four an IRS notice arrives at an old US address the client has not held for a decade, because no representative was ever recorded to receive copies. The certification narrative has to be redrafted because the facts moved. A case that should have completed inside a quarter runs past three, and the client spends that time exposed.

The technical work in both versions is identical. The difference is entirely the authorisation layer. Our IRS streamlined filing specialists treat it as the critical path, because it is.

Authority for entities, trusts and estates

Individual authorisations do not extend to entities you own or control. Each requires its own instrument, and this is where cross-border cases become genuinely intricate.

• UK companies with US owners. A Form 5471 obligation attaches to you personally as a shareholder, so it travels on your individual authorisation. The company's own UK corporation tax affairs require a separate HMRC authorisation in the company's name.
• Trusts. A trust with US connections may generate reporting obligations for the trust, the trustees and the beneficiaries, each potentially requiring distinct authority. On the UK side, Trust Registration Service access is granted only by digital handshake, completed by the lead trustee. Our trusts and estate planning team maps these before work starts.
• Estates and incapacity. Where a taxpayer has died or lacks capacity, ordinary authorisation forms do not apply. A fiduciary notice is used in the US to establish the fiduciary relationship, and HMRC has separate personal representative processes. A power of attorney granted under English law is not automatically effective for IRS purposes, and assuming otherwise costs months.
• Partnerships and LLCs. Authority is required at entity level, signed by a person with binding authority for the entity — which must itself be evidenced.

What should you ask a firm before you engage?

Five questions will tell you, in under ten minutes, whether a firm actually runs cross-border catch-ups or merely advertises them.

• Who on the team holds unlimited IRS practice rights, and will that person be named on my Form 2848? A firm that cannot name the individual is telling you something.
• Will you pull my IRS transcripts before quoting? If the answer is no, the quote is a guess and will change.
• Which HMRC authorisation route applies to each of my taxes, and which need a digital handshake? A specific answer means they have mapped it. A vague answer means they will discover the CGT-on-property or trust route halfway through.
• How will you handle authorisation given I have no UK postcode? A firm with real non-resident experience will describe the paper route and the timescale without hesitation.
• Which documents will I have to sign personally, and when? A credible firm produces a list. It should include the certification, the e-file authorisations and the FBAR authorisation.

Common authorisation mistakes in cross-border catch-ups

• Assuming a UK accountant's 64-8 covers the US side. It covers nothing outside HMRC, and nothing outside the taxes listed on the form.
• Assuming a Form 2848 covers FBAR filing. It does not authorise e-filing the report; the 114a does.
• Specifying too few years. A six-year delinquency needs authorisation across the full window plus the surrounding filed years.
• Letting a digital handshake expire. The invitation window is short, the email is easily missed, and the process restarts from the beginning.
• Leaving a stale address of record. Notices and activation codes go to the address the authority holds, not the one you use now. Correcting it is a prerequisite, not an afterthought.
• Failing to revoke a previous adviser's authority. Old authorisations can persist, sending notices to a firm no longer instructed and creating genuine confusion about who is acting.
• Sharing Government Gateway credentials. Never appropriate, and a clear signal about a firm's standards.

The sequencing playbook

For a typical dual-filer catch-up, the order of operations that works is consistent enough to be a template. Sign the US information authorisation first and pull transcripts, because everything else is scoped from what they reveal. Initiate the UK authorisation in parallel on day one rather than waiting for the US diagnosis, since the UK route may be the slower of the two. Confirm and correct the addresses of record on both sides before anything else is submitted. Establish the representation authority for the specific years and matters where a challenge is plausible. Complete the FBAR filing authorisation before the reports are prepared, not after. Only then commit to a scope, a fee and a timetable.

Run in that order, the authorisation layer costs perhaps two to three weeks of elapsed time and almost no client effort. Run out of order, it is the reason a case that should close in a quarter is still open a year later. You can read more on how we structure cross-border engagements across our guides and our US-UK tax accountants practice.

Speak to us before you sign anything

If you are weighing a multi-year US-UK catch-up — missed returns on either side, unfiled FBARs or Forms 8938, an unreported UK pension or ISA, a company or trust nobody has considered from the US perspective — the authorisation layer is where the engagement is won or lost. We will tell you exactly which permissions your position requires, what you will need to sign personally, and how long each will realistically take, before you commit to anything. To discuss your position in confidence, contact our cross-border team for a private consultation with a specialist who holds authority on both sides.