Compliance
Mandatory Registration for UK Tax Advisers: What It Means & How to Comply
From 18 May 2026 a new requirement—MMTAR—makes registration mandatory for tax advisers dealing with HMRC on behalf of clients. Here’s how it affects you and your clients.
By NomadicTax Research Team • 5-8 min read • June 2, 2026
## What is the MMTAR rule?
The UK government has introduced **MMTAR** (Modernising and Mandating Tax Adviser Registration). As of 18 May 2026, any tax adviser who **receives payment to interact with HMRC on behalf of clients** must register online under this new scheme. This replaces previous agent registration processes, aiming to simplify the system and raise professional standards. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Who needs to register—and when?
MMTAR rolls out in **phases**. You will need to register if you fall into one of these categories, during the specified window:
| Time Period | Who Must Register |
|-------------|--------------------|
| 18 May-18 August 2026 | New tax advisers and those interacting with HMRC but without any 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-18 November 2026 | Advisers who have a Self Assessment or Corporation Tax account 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 2026-18 February 2027 | Advisers whose only business is 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 2026-31 March 2027 | Advisors already holding an ASA and financial services organisations. Exact definitions to be provided. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))|
## How to register: Key Requirements
You'll need to prepare the following to complete registration:
- Government Gateway user credentials (ID and password)
- Your firm’s UTR and associated postcode
- Company registration number, if applicable
- VAT registration number, if applicable
- National Insurance number and date of birth (for sole traders, partnerships, or LLPs)
- Details of your Anti-Money Laundering supervisory body (name, membership, renewal date)
Note: Advisers acting informally (e.g., unpaid community advice) may be exempt. Custom and excise intermediation activities may also have exemptions. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Risks of non-registration & action steps
Failure to register by your deadline means **you cannot legally interact with HMRC** in your adviser role—and you may face sanctions, including loss of ability to act and financial penalties. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
### What you can do now:
- Determine which phase applies to you based on your current registration status.
- Visit GOV.UK to use their interactive checker tool to confirm whether registration 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 documents (UTR, NI, etc.) ahead of your registration window.
- If you use agents or have clients who rely on you, inform them about changes that may affect the continuity of your representation of them with HMRC.
## Practical example
Sarah is a self-employed tax adviser who helps small business clients with Corporation Tax filings and has a self assessment account but **does not yet have** an ASA. She must register between **18 August and 18 November 2026**. If she had only payroll service clients, her window would be **18 November 2026 to 18 February 2027**. If she fails to register within her window, she may no longer represent clients.
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Making sure you comply with MMTAR isn’t just about following rules—it protects clients, boosts credibility, and maintains trust with HMRC. **Get on top of it early to avoid last-minute scramble or service disruption.**