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)
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 | |
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)
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)
Penalties and obligations
- Registration is free, but mandatory for those who interact with HMRC for tax advice or related services.(mynewsdesk.com)
- 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.
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.