Background
On 14 May 2026, the UK government confirmed that paid tax advisers interacting with HMRC on behalf of others must register with HMRC’s new Modernising and Mandating Tax Adviser Registration (MMTAR) system. The rollout begins 18 May 2026 and continues in phases until 31 March 2027. (gov.uk)
What You Must Do—and By When
| Phase | Who is in scope | Registration window |
|---|---|---|
| Phase 1 (18 May - 18 Aug 2026) | New advisers, or those working without an Agent Services Account (ASA), Self Assessment or CT account | 18 May – 18 August 2026 |
| Phase 2 (18 Aug ‐ 18 Nov 2026) | Advisers with SA/CT account but without an ASA | 18 August – 18 November 2026 |
| Phase 3 (18 Nov 2026 – 18 Feb 2027) | Advisers with payroll-only services | 18 November – 18 February 2027 |
| Final Window (31 Dec 2026 – 31 Mar 2027) | Still to be confirmed in detail | 31 December 2026 – 31 March 2027 |
Registration is free, and there’s new digital tools, including an interactive checker to see if you need to register. (gov.uk)
Who Is—and Who Isn't—Required
✔ Required
- Any adviser paid to interact with HMRC on behalf of clients: writing letters, handling appeals etc.
- Advisers that don’t have an ASA but are acting under Self Assessment or Corporation Tax obligations.
✖ Exemptions include
- Voluntary sector organisations when not acting in a business capacity.
- Advisors who don’t provide tax advice as a business.
Implications & Benefits
- Higher standards and accountability: Easier for HMRC and clients to know who is regulated.
- Uniform way to prove credentials: ASA becomes core to adviser-client interactions.
- Overseas advisers who deal with UK tax issues must also register if getting paid.
Practical Advice for Tax Advisers
- If you haven’t already, check the guidance and ascertain your category. Use the interactive checker tool on GOV.UK.
- Prepare documents: UTR, company registration number, VAT registration, NI number etc. (these are required to register). (gov.uk)
- Educate clients: ensure they understand where they can verify you via the new registry to build trust.
- Budget time: phase-by-phase windows mean deadlines matter; missing your window could restrict ability to act for clients.
Final Thoughts
Though this policy shifts administrative burden to advisers, it strengthens professional reputation and safeguards clients. Getting registered early, understanding the rules, and keeping up with guidance releases will be key.