Mandatory HMRC tax adviser registration began on 18 May 2026 and runs in staged windows to 31 March 2027. How to check your accountant is registered, AML-supervised and genuinely qualified.
Since 18 May 2026, anyone paid to interact with HMRC about someone else's tax affairs must be registered with HMRC and meet minimum conditions before they can act for you. Registration is phased in through four three-month windows running to 31 March 2027, and HMRC can suspend, penalise or bar advisers who do not comply. That turns a vague question — "is my accountant any good?" — into three checkable facts: are they registered, are they supervised for anti-money laundering, and can they evidence the qualification they advertise?
The programme is Modernising and Mandating Tax Adviser Registration (MMTAR). It replaces a patchwork of older agent registration routes with a single digital registration built around the agent services account. The powers, including the sanctions regime, sit in Part 7 of the Finance Act 2026, with statutory exceptions in Schedule 20 and SI 2026/815.
Registration is free and online; HMRC reported more than 4,000 applications in the first window. The aim is to raise standards in the tax advice market — which only helps you if you actually check.
| Window | Which advisers register in it |
| --- | --- |
| 18 May to 17 August 2026 | New advisers, and anyone interacting with HMRC without an ASA, Self Assessment or Corporation Tax account |
| 18 August to 17 November 2026 | Advisers with a Self Assessment or Corporation Tax account but no ASA |
| 18 November 2026 to 17 February 2027 | Advisers who solely provide payroll services and have no ASA |
| 31 December 2026 to 31 March 2027 | Financial services organisations without an ASA |
A business providing more than one type of service registers in the earliest window that applies: a payroll bureau that also prepares Self Assessment returns cannot sit in the payroll tranche. Firms that held an ASA before 18 May 2026 are being migrated to the new digital service by 31 March 2027 without a fresh application.
HMRC treats a business as a tax adviser if it interacts with HMRC about another person's tax affairs and is paid for it. Interaction covers telephone, post and email, messages through the GOV.UK website or the HMRC app, making payments, and sending returns, claims or other documents. The legal entity registers, not each employee.
The requirement bites even where a firm does not think of itself as a tax practice: where it does not describe its work as tax advice, where it operates as a sole trader, where tax is not the main business function, and even where it acts for only one client. It applies to businesses based outside the UK acting for UK taxpayers.
The carve-outs are narrower than people assume. A business is outside the requirement if it only interacts with HMRC:
Mixed activity does not rescue anyone. If part of what a firm does is in scope, the firm registers.
Registration is not a formality. The business must provide evidence that it is supervised for anti-money laundering, and it must not:
The same conditions apply to the firm's "relevant individuals" — those who decide how the business manages or organises its tax adviser work — though they need not supply AML evidence themselves. Where a business has five officers or fewer, HMRC treats all of them as relevant individuals; where it has six or more, the firm names those making strategic or management decisions about its tax work, and at least five in total.
There is a quiet but important point in that list: a firm whose own tax affairs are not in order cannot register to run yours. Overseas advisers must additionally supply notarised and, where necessary, translated evidence.
Every UK business providing accountancy or tax services to third parties must be supervised for money laundering purposes by a named authority. That supervision is where client due diligence, record-keeping standards and suspicious activity reporting obligations come from, and it is now the entry ticket to HMRC registration.
Supervision comes from one of two places. If the firm belongs to a professional body, that body usually supervises it; HMRC names fourteen, including ACCA, ICAEW, ICAS, Chartered Accountants Ireland, the Chartered Institute of Taxation, the ATT, the AAT, CIMA and the Law Society.
If the firm belongs to none of them, it must register with HMRC for supervision and pay an annual fee. That answers the question clients rarely know to ask: who supervises an accountant who is in no professional body? HMRC does — and you can look it up. The Supervised Business Register on GOV.UK can be searched by business name, trading name, individual name or registration number, and shows the registration number, part of the postcode, the date supervision began and the sectors covered. HMRC notes there can be a delay before a newly registered business appears, so a blank result for a recently formed firm is a prompt to ask, not proof of anything.
AML supervision must also already be in place before tax adviser registration can complete. An application in progress does not count.
Work down this once; it takes less than half an hour.
| What to check | Where to check it | What a good answer looks like |
| --- | --- | --- |
| HMRC tax adviser registration | Ask the firm: which window applied, and do you hold an agent services account? | They hold an ASA, or held one before 18 May 2026. A firm in the first or second window still "looking into it" is a red flag |
| AML supervision | HMRC's Supervised Business Register, or the professional body's register | A named supervisor and registration number, with the certificate on request |
| Professional body membership | The body's public register of members and firms | The individual doing your work appears, not only a founder or parent company |
| Practising certificate | Ask the firm | Confirmation they hold one. Membership is not authorisation to practise publicly |
| Professional indemnity insurance | Ask for the insurer and limit of indemnity | A current policy, with a limit proportionate to your affairs |
| Use of protected titles | Compare the claimed title against the body that awards it | "Chartered Certified Accountant" means ACCA; "Chartered Accountant" means ICAEW, ICAS or Chartered Accountants Ireland; "accountant" alone tells you nothing |
| Who signs the filing | Ask for a name and a credential | A named, qualified individual who reviews and signs — not "the team" |
| US credentials, if you file in both countries | The IRS directory of federal tax return preparers | A valid PTIN plus an Enrolled Agent, CPA or attorney credential |
1. Do you hold an agent services account, and which registration window applied to your firm?
2. Who supervises you for anti-money laundering, and what is your supervision registration number?
3. Which professional body are you a member of, and do you hold a practising certificate?
4. What professional indemnity cover do you carry, and with which insurer?
5. Who personally reviews and signs my return, and what credential do they hold?
A firm that answers all five in a short email tells you something useful. A firm that cannot, or will not, is also telling you something.
HMRC's guidance illustrates how the windows work. Take an accountancy firm holding Corporation Tax and Self Assessment agent codes but no agent services account. It falls in the second tranche, so its deadline is 18 November 2026. It applies on 16 November 2026 — inside the window — and HMRC does not approve it until 3 January 2027.
Because the application went in before the deadline, the firm may keep interacting with HMRC for clients while it is processed, and is not treated as unregistered merely because the decision is outstanding. Once approved, the conditions apply from the date registration takes effect.
The lesson for clients is narrow but useful: a firm that applied on time is fine even if the paperwork is still moving. A firm that let the date pass is not.
HMRC registration tests integrity and supervision. It does not test technical competence, and it is not a qualification. That comes from elsewhere, and terminology matters.
In the UK, "accountant" is not a protected title. Anyone may use it, qualified or not. What is protected are the chartered designations, and they are not interchangeable. The UK regulated professions service records Chartered Certified Accountant as a legally protected term restricted to ACCA members under the body's Royal Charter, with members in public practice additionally required to hold a practising certificate, carry liability insurance and submit to inspection. Separately, Chartered Accountant — with the designations ACA, FCA and CA — is protected for members of ICAEW, ICAS and Chartered Accountants Ireland. Two titles, different bodies and examinations; neither is implied by the word "accountant".
Professional indemnity insurance is the third layer. HMRC does not check it at registration, but professional bodies generally require it of firms in public practice, and it is what stands between you and an uninsured error. Ask for the limit, not just confirmation that a policy exists. If you are choosing a firm rather than vetting one, our guide on how to choose an accountant for a cross-border business covers the commercial questions.
This is where clients most often get caught out. A UK adviser's credentials say nothing about their right to act before the IRS, and a US preparer's say nothing about their standing with HMRC. The systems are separate, and the new HMRC rules do not change that.
On the US side, the IRS explains that anyone paid to prepare a federal return must hold a Preparer Tax Identification Number (PTIN), and that only three groups hold unlimited representation rights before the IRS:
Those rights mean the practitioner can act for you on audits, payment and collection issues and appeals, whether or not they prepared the return. A preparer holding only a PTIN may prepare a return and nothing more.
On the UK side, what counts is membership of a recognised professional body — ACCA, ICAEW, ICAS, Chartered Accountants Ireland, CIOT, ATT and the others above — plus a practising certificate, AML supervision, and now HMRC registration.
So a US Enrolled Agent has no particular standing with HMRC, and a UK accountant has no right to represent you before the IRS without a US credential. If you file in both countries you need both sides covered, by one person who holds both or two who speak regularly. We set this out across our work on accountants for US and UK filers, and in our guide to US tax compliance for Americans abroad.
On our own position: at Next Tax Source every filing is reviewed and signed by a licensed professional, and the practitioner who signs US work is an IRS Enrolled Agent who is also ACCA-qualified — see our about page. We are not a chartered firm and we do not describe ourselves as one.
Sanctions have been available since 18 August 2026. HMRC's framework includes suspension of registration, financial penalties, ineligibility orders, and publication of details about sanctioned advisers where legislation permits. Suspension is the one that reaches you directly: a suspended adviser loses access to the relevant HMRC services and cannot carry out in-scope interactions for you.
The timing is more forgiving than the headline suggests. Interactions before 18 August 2026 cannot give rise to a sanction for unregistered activity, and an adviser who misses their window can only be sanctioned from the date registration became mandatory for their tranche. HMRC says it will give advisers the chance to correct problems first, and there are rights of review and appeal.
None of that transfers risk away from you. If your agent is suspended mid-year, your Self Assessment or corporation tax return is still due on the same date, and you will need to appoint and authorise someone else — which takes time you may not have in January.
1. Ask in writing, with a date for a reply, and keep the email.
2. Check the Supervised Business Register and the professional body register yourself, rather than relying on a logo on a website.
3. Request copies of your own records and filed returns now, not later. You are entitled to them.
4. If no answers come, appoint a replacement and complete fresh agent authorisation before the next deadline.
5. Review the last few years of filings with the new adviser. Where a firm could not meet basic integrity conditions, the technical work deserves a look too — our guide to who must file a Self Assessment return is a sensible baseline.
Most people will run these checks, get sensible answers and carry on. The cases worth a second opinion are where answers are vague, where your adviser's registration status is still unclear this close to filing season, or where you file in more than one country and no single person can say who owns which return. If that sounds familiar, book a consultation and bring whatever your current adviser has given you — the quickest way to find a gap is to look at the last two years of filings side by side.
This article is general information about UK and US rules as they stand on 1 October 2026. It is not advice on your own circumstances.