From 18 August 2026, a tax adviser in the first tranche of HMRC’s new registration regime may not interact with HMRC about a client’s tax affairs unless the firm is registered or a Schedule 20 exception applies. Section 223 of the Finance Act 2026 defines interacting widely: contact by telephone, post or email, a message through a website or portal, the filing of “a return, claim, notice or other document”, or communicating “in any other way”. A phone call about your corporation tax position is caught. So is filing your Additional Information Form.
The definition of “tax adviser” reaches R&D consultancies directly. Section 224 covers any organisation or sole trader that assists other persons with their tax affairs, including one that “provides assistance with any document that is likely to be relied on by HMRC to determine the other person’s tax position”. An R&D report and an AIF are exactly that.
When does it actually apply?
Two timetables run three months apart, and confusing them is the most common error in what has been written about this. HMRC’s guidance gives the dates on which the registration service opens for each group of advisers. SI 2026/807, the commencement regulations made on 13 July 2026, gives the dates on which the section 223 prohibition comes into force for each group. They are not the same dates and they do not do the same job.
| Tranche | Who is in it | Registration window opens | Registration required from |
|---|---|---|---|
| First | Every adviser not in a later tranche — including all Agent Services Account holders, and advisers setting up from new | 18 May 2026 | 18 August 2026 |
| Second | Advisers with a Self Assessment or Corporation Tax agent account but no Agent Services Account | 18 August 2026 | 18 November 2026 |
| Third | Payroll-only agents without an Agent Services Account | 18 November 2026 | 18 February 2027 |
| Fourth | Financial services organisations without an Agent Services Account | 31 December 2026 | 1 April 2027 |
The window-opening dates come from HMRC’s guidance page; each window runs for three months. The dates in the final column are the appointed days set by regulation 4 of SI 2026/807, when Chapter 1 of Part 7 of the Finance Act 2026 comes into force for that tranche.
Firms that already hold an Agent Services Account sit in the first tranche as well. The regulations define every other tranche by the absence of an ASA immediately before 18 August 2026, so ASA holders fall into the first by construction. They do not apply for anything; the regulations register them.
Why is everyone unsure of the date?
Because the start date moved twice, and neither move was presented as a change.
April 2026 was stated and restated. The consultation response of October 2024 said the requirement would apply from April 2026. The policy paper of 21 July 2025 said it “will begin from 1 April 2026, with a transitional period of at least 3 months”, and the written ministerial statement that day said the changes would take effect from April 2026. Clause 22(2) of the draft Bill hard-coded 1 April 2026 on the face of the legislation.
That date did not survive enactment. The fixed commencement date was removed, and section 249(2) of the Act as passed leaves commencement entirely to Treasury regulations. The Budget 2025 policy paper, published on 26 November 2025, then said it would “begin in May 2026”. No correction note, no acknowledgement that the date had moved.
The July 2025 policy paper is still live, still unamended, still saying 1 April 2026. HMRC’s press release of 20 July 2026 groups existing Agent Services Account holders into the 31 December 2026 to 31 March 2027 window, which describes the administrative contact HMRC intends to make but reads against regulations 4 and 5 on their face. And the guidance page never once uses the word “deadline”. It gives the date each window opens, states that each runs three months, and leaves the reader to do the arithmetic.
What it means for an established firm
Regulation 5 does the work for anyone who already holds an ASA. Where a tax adviser has an Agent Services Account immediately before 18 August 2026, the Act applies to them as if they had applied for registration, as if that application had been approved, and as if they had been notified that registration took effect from 18 August 2026. No form. No fee. There is no renewal, no annual return and no periodic confirmation anywhere in Part 7.
Something does follow later. HMRC expects to contact existing ASA holders in early 2027 to collect the names of the firm’s relevant individuals and evidence of anti-money-laundering supervision. ICAEW has confirmed that HMRC will accept a screenshot of a firm’s entry on the find-a-chartered-accountant register as proof that ICAEW supervises it.
For advisers who do have to apply, the enforcement ladder is gentler than the coverage suggests. A first contravention carries no penalty. HMRC must notify the adviser and allow 30 days for representations before issuing a compliance notice, and the £5,000 penalty under section 234 only arrives on a further contravention. Registering afterwards cures it: section 233(5) treats a compliance notice as withdrawn where the adviser was unregistered at the time and subsequently registers. Agent Update 145, published on 16 July 2026, goes further, and says that businesses relying on HMRC guidance in good faith to decide they do not need to register will be treated as compliant, with no sanctions or penalties, even if HMRC later clarifies that they should have registered.
The register that does not exist
Part 7 creates no register, no list and no lookup. HMRC notifies the adviser that the registration has effect, and that is the end of it. The Act does contain publication powers, three of them, and every one is aimed at failure: section 246 covers penalties and ineligibility orders, and sections 251 and 252 cover refusals to deal and suspension of online access. Powers to publish the delinquent, and no power to publish the compliant.
Registration is invisible. Only failure is publishable. A company cannot look up whether its adviser is registered. It can only ask.
The answer would tell you less than it sounds like it tells you, in any event. HMRC’s own fact sheet of 14 May 2026 says registration “is not a form of regulation and does not reflect your competency or authorise you to advise on tax matters”. Registration is free, and HMRC says it should take no more than an hour.
What a company should check instead
The same things as before, which is rather the point. The verifiable signals are the ones that were always verifiable.
- The professional bodies’ public registers. ICAEW’s find-a-chartered-accountant register lists both firms and the chartered accountants in them, and CIOT keeps a directory of Chartered Tax Advisers. A claimed qualification can be checked in minutes.
- AML supervision. Ask who supervises the firm for anti-money-laundering purposes. It is a legal requirement, and a supervised firm answers in one sentence.
- Who signs the claim. The named, qualified person who reviews the work and signs it off.
- Whether enquiry support sits in the engagement letter. Ask what happens if HMRC opens an enquiry into a claim the firm prepared, and check that the answer appears in writing.
The fuller treatment, including the questions to ask and the red flags, is on how to choose an R&D tax adviser.
One gap is worth knowing about. The registration requirement catches only firms that interact with HMRC. A boutique that writes the R&D report and leaves the client’s own accountant to file it never contacts HMRC, and falls outside the regime entirely. It stays caught by the money laundering regulations, which define a tax adviser by the provision of “material aid, or assistance or advice” on another person’s tax affairs and require no HMRC contact at all. Trading without that supervision has been a criminal offence since 2017, carrying up to two years’ imprisonment. Two registers, different nets.
Where LimestoneGrey sits
LimestoneGrey is a long-established registered agent with an Agent Services Account, so the firm falls in the first tranche and is treated as registered from 18 August 2026 under the transitional rule; it is supervised by ICAEW for anti-money-laundering purposes, and its ICAEW record is public, so the part that can be checked can be checked. How we are regulated is set out in full on our regulation and standards page.
If you are reviewing who prepares your claims, start a conversation with a chartered adviser.
Sources
- Finance Act 2026, section 223 — the prohibition on interacting with HMRC while unregistered, and what counts as interacting.
- Finance Act 2026, section 224 — who counts as a tax adviser, including a person who “provides assistance with any document that is likely to be relied on by HMRC to determine the other person’s tax position”.
- The Finance Act 2026 (Registration of Tax Advisers) (Appointed Days and Transitional Provision) Regulations 2026, SI 2026/807 — the appointed days for each tranche in regulation 4, and the automatic registration of Agent Services Account holders in regulation 5.
- Check if and when you need to register as a tax adviser with HMRC — HMRC’s guidance, giving the date each registration window opens and the three-month rule.
- Finance Act 2026, section 246 — the power to publish details of penalties and ineligibility orders under Chapter 1.
- Modernising and mandating tax adviser registration with HMRC — HMRC policy paper, 21 July 2025: “This will begin from 1 April 2026, with a transitional period of at least 3 months.” Still live, unamended, no correction note.
- Mandatory tax adviser registration with HMRC — Budget 2025 policy paper, 26 November 2025: “This will begin in May 2026, with a transitional period of at least 3 months for all tax adviser groups.” Published without a correction note.
- Tax advisers: one month left to register under new rules — HMRC press release, 20 July 2026: registration opened on 18 May 2026, and the first registration window closes on 18 August 2026.
- Mandatory tax adviser registration communications resources: fact sheet — HMRC, 14 May 2026: registration is free, “should take no more than an hour”, and “is not a form of regulation and does not reflect your competency or authorise you to advise on tax matters”.
- The Money Laundering Regulations 2017, regulation 86 — trading without required anti-money-laundering registration as a criminal offence, with imprisonment of up to two years on conviction on indictment.
- Agent Update 145, HMRC, 16 July 2026 — businesses relying on HMRC guidance in good faith to decide they do not need to register will be treated as compliant.
This article describes the rules as they stood at the review date above. The rules change: for the current position, start with our guides or talk to us.
