Compliance
Navigating the New Tax Adviser Registration Rules (MMTAR)
The UK has introduced mandatory registration for tax advisers starting 18 May 2026—this article helps practitioners and clients understand who is affected, how to comply, and what risks to avoid.
By NomadicTax Research Team • 5-8 min read • June 7, 2026
## What is MM TAR?
MMTAR stands for *Modernising and Mandating Tax Adviser Registration*. From **18 May 2026**, anyone paid to interact with HMRC on behalf of someone else must register as a tax adviser. Key goals are to raise standards, protect taxpayers, and clarify accountability. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Who must register and when
Registration is staged by adviser type through **18 May 2026 to 31 March 2027**:
- From 18 May 2026: new advisers, or those without any existing ASA, Self Assessment or Corporation Tax account.
- From 18 August to 18 November 2026: advisors with a Self Assessment or Corporation Tax account but no ASA.
- From 18 November 2026 to 18 February 2027: advisers providing only payroll services.
- Phase out or full compliance expected 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))
## Action steps for advisers and clients
**For tax advisers:**
- Check whether your work requires registration (paid interaction with HMRC, acting as agent). Exemptions include unpaid voluntary roles and certain non-business advice roles. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- Prepare documentation: Government Gateway ID, UTR, company number, if applicable, identity verification (NI number/DOB).
- Use new *interactive checker tool* on GOV.UK to see when your registration window opens.
- Plan to convert your operations to use the Agent Services Account (ASA), if not already using it.
**For clients of advisers:**
- Confirm adviser is registered under MM TAR. Ask for registration number or ASA credentials.
- If working with overseas advisers, ensure they comply if they represent your UK tax affairs—non-compliance could expose you to risk.
## Risks, penalties and compliance
- Failing to register when required may prevent an adviser from interacting with HMRC on behalf of clients.
- **Clients** using unregistered advisers may face issues if HMRC doesn’t accept communications through them.
- Incorrect or incomplete registration could lead to delays in dispute resolutions, filings, or seeking reliefs.
## Example case
Sarah is a sole trader who hires an overseas tax agent to submit her Self Assessment. Even though the adviser is overseas, because they’re being paid to interact with HMRC on Sarah’s behalf, they must register under MM TAR. Sarah should confirm registration before engaging the agent.
## What this means long-term
- Clients will have clearer paths to verify adviser credentials.
- HMRC regulatory enforcement may increase for fraud or misrepresentation by advisers.
- Standards in tax advice likely to tighten, with expectations for professionalism and compliance increasing.
**Takeaway:** If you're paid to advise or act on someone else's tax affairs in the UK, you must register under MMTAR. Start soon—as windows are open and requirements become mandatory.