Compliance
New MMTAR Rules: What UK Tax Advisers Need to Do by Spring 2027
HMRC’s Modernising and Mandating Tax Adviser Registration (MMTAR) imposes sweeping new registration requirements—know the deadlines and criteria to avoid penalties.
By NomadicTax Research Team • 5-8 min read • June 1, 2026
## What is MMTAR?
**MMTAR (Modernising and Mandating Tax Adviser Registration)** is a regulatory overhaul introduced by HMRC. Its goals are:
- Higher standards in the tax advice market
- Clearer accountability and visibility of tax advisers
- Protection of taxpayers from bad advice or unregistered agents.
This overhaul was originally announced at **Budget 2025**, following public consultation. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Key timelines and who is affected
| Period | Which advisers must register | Details |
|---|---|---|
| **From 18 May to 18 August 2026** | New tax advisers, or those interacting with HMRC without an **Agent Services Account** (ASA), Self Assessment or Corporation Tax account. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai)) |
| **18 August to 18 November 2026** | Advisers with Self Assessment or Corporation Tax accounts but **without** an ASA. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai)) |
| **18 November 2026 to 18 February 2027** | Advisers solely providing payroll services. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai)) |
| **31 December 2026 to 31 March 2027** | Those with existing ASAs and financial services organisations. Definition and criteria to be specified. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai)) |
Advisers will have **three months** from the start of their registration window to apply. During this period, they can continue working with clients while the registration is pending. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## What you must do to qualify
To register under MMTAR and hold an ASA, you must meet specific conditions:
- Provide identity information: name, date of birth, National Insurance number. If you run a business, company registration and VAT identification are required. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- If applicable, submit information about your **anti-money laundering (AML) supervisory body**, including membership number and renewal date. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- Only those **paid to interact with HMRC about someone else’s tax affairs** count as ‘tax advisers’ under the rules. Some activities are exempt. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Compliance and penalties
Acting without registration when required could lead to **sanctions**, possible financial penalties, and being barred from representing clients with HMRC. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Action plan for advisers
- Check the guidance on GOV.UK and determine which of the phased windows applies to you. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- Gather required documentation: ASA, UTR, company/VAT registration, AML body info if needed.
- Apply during your window to avoid disruption.
- Inform clients proactively if your registration or standing changes in the registration process.
## Bottom line
MMTAR marks a big change in how tax advisers must operate in the UK. If you're a paid adviser, interacting with HMRC, or planning to do so, get ahead now. Missing your registration deadline could lead to serious consequences for you and clients.