Compliance
How Modernising Tax Adviser Registration (MMTAR) Affects You
Starting 18 May 2026, tax advisers who interact with HMRC on behalf of clients need to register under a new regime—learn who's impacted, how to comply, and avoid penalties.
By NomadicTax Research Team • 5-8 min read • May 18, 2026
## What is the MMTAR regime?
From **18 May 2026**, the UK government introduces **Modernising and Mandating Tax Adviser Registration (MMTAR)**. Any individual or firm paid to interact with HMRC on behalf of clients must register through the streamlined digital system.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
### Staged rollout timeline
- 18 May to 18 August 2026: new advisers or those without an Agent Services Account (ASA) interacting in Self Assessment or Corporation Tax matters.([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 who have SA/Corp Tax accounts but no 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: payroll-only advisers.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- By **31 March 2027**, remaining advisers (including those with ASA, financial services entities) must be registered.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
### What registration involves
- Applying for or ensuring you have an **Agent Services Account**.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- Providing identity verification (NI number, DOB) if a sole trader, partner, or LLP.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- Supplying any existing UTR (Unique Taxpayer Reference), VAT number, company registration number where relevant.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- Registering is **free**, and exemption exists for those not receiving payment or not acting as professional advisers.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Why it matters
- **Protecting taxpayers**: makes it clearer who is providing advice, enhancing accountability.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- **Raising standards**: standardization aims to reduce poor advice in the tax market.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- **Market fairness**: ensures all professional advisers comply with similar requirements.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Who is impacted
- Any person or firm that is paid to **interact with HMRC** on behalf of clients about tax matters.
- Includes advisers based overseas interacting on UK taxpayer’s behalf.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- Those already holding ASA do **not** need to re-register unless new data or conditions are required.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Actionable steps
1. Check **if and when** you must register using HMRC’s checker tools.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
2. If not already done, set up an **Agent Services Account**.
3. Collect needed documentation: company / VAT registrations, proof of identity.
4. Understand client service obligations under registration and maintain records.
5. Stay aware: different phases have deadlines; missing registration may affect ability to act for clients and potentially lead to penalties.
## Example scenarios
| Situation | Do you need to register from 18 May 2026? |
|---|---|
| Newly qualified accountant offering Corporation Tax advice, no ASA yet | **Yes** – within first window.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai)) |
| Established accountant with ASA, interacting via Self Assessment and Corporation Tax | **Later windows apply**; final registration must by **31 March 2027**.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai)) |
| Payroll specialist only dealing with payroll services | Register between **November 2026 and February 2027**.([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai)) |
By adjusting your processes now, you'll be ready for registration and able to continue representing clients without interruption.