Compliance
Mandatory Tax Adviser Registration (MMTAR): What UK Advisers Need to Do Now
From 18 May 2026, UK tax advisers interacting with HMRC on behalf of clients must register under new rules — here's who, when, and how.
By NomadicTax Research Team • 5-8 min read • June 8, 2026
## What is MMTAR?
The UK government introduced **Modernising and Mandating Tax Adviser Registration (MMTAR)** to standardise the tax advice market. It requires tax advisers who interact with HMRC on clients’ behalf to **register formally**, giving certainty to clients and ensuring consistent standards across the profession.([mynewsdesk.com](https://www.mynewsdesk.com/uk/hm-revenue-customs-hmrc/pressreleases/tax-advisers-check-if-you-need-to-register-under-new-rules-3448457?utm_source=openai))
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## Who is in scope and when does it apply?
| Adviser type | Roll-out window | Key date |
|---|---|---|
| New tax advisers, or advisers without an Agent Services Account (ASA) for Self Assessment/Corporation Tax | 18 May – 18 August 2026 | **Must register between these dates** to apply for ASA |
| Advisers with a Self Assessment or Corporation Tax account but without ASA | 18 August – 18 November 2026 | Transition period for registration |
| Advisers who provide payroll-only services | 18 November 2026 – 18 February 2027 |
| Existing ASAs & financial services organisations | 31 December 2026 – 31 March 2027 |
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If you miss your group’s registration window, HMRC offers **three months** from its open date to apply without losing client service ability.([mynewsdesk.com](https://www.mynewsdesk.com/uk/hm-revenue-customs-hmrc/pressreleases/tax-advisers-check-if-you-need-to-register-under-new-rules-3448457?utm_source=openai))
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## What you need to do step by step
- Check whether you need to register using the interactive tool on GOV.UK.
- Prepare information: Government Gateway user ID, UTR (Unique Taxpayer Reference), business postcode, company/VAT registration if applicable.
- If you are a sole trader or partnership, you may also need your National Insurance number and date of birth. If supervised for anti-money laundering (AML) purposes, supply supervisory body details.([mynewsdesk.com](https://www.mynewsdesk.com/uk/hm-revenue-customs-hmrc/pressreleases/tax-advisers-check-if-you-need-to-register-under-new-rules-3448457?utm_source=openai))
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## Penalties and obligations
- Registration is **free**, but mandatory for those who interact with HMRC for tax advice or related services.([mynewsdesk.com](https://www.mynewsdesk.com/uk/hm-revenue-customs-hmrc/pressreleases/tax-advisers-check-if-you-need-to-register-under-new-rules-3448457?utm_source=openai))
- From the start of each group’s window, clients should verify that their advisers are registered; using an unregistered adviser may cause issues with HMRC dealings.
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## Practical tips
- If you’re just above de minimis thresholds or expect lower claims this year, aim to register early.
- Maintain proof of registration – include ASA details in correspondence and marketing.
- Consider joining professional bodies that have oversight for AML, as this requirement is part of registration.
The MMTAR regime represents one of the **biggest regulatory shifts for UK tax advisers in decades** — not just in compliance but also in public trust. Address it proactively rather than reactively.