Compliance
Navigating the New Mandatory Tax Adviser Registration Regime in the UK
From mid-May 2026, all paid tax advisers interacting with HMRC must register under the Modernising and Mandating Tax Adviser Registration (MMTAR) scheme. This article explains what this means for advisers and clients, and how to comply.
By NomadicTax Research Team • 5-8 min read • May 31, 2026
## What is the Modernising and Mandating Tax Adviser Registration (MMTAR)
In May 2026, HMRC introduced new **mandatory registration requirements** for tax advisers who are paid to interact with HMRC on behalf of clients. This reform, known as **MMTAR**, aims to raise standards, protect consumers, and streamline adviser-client relationships. It's being implemented in phased windows between **18 May 2026** and **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))
## Who must register and when
HMRC has grouped advisers into cohorts each with their own deadline to register under the new system:
| Cohort | When they must register | Who is included |
|---|---|---|
| *18 May – 18 Aug 2026* | New advisers or those without an Agent Services Account (ASA), Self Assessment or Corporation Tax account. |
| *18 Aug – 18 Nov 2026* | Advisers with a Self Assessment or Corporation Tax account, but without an ASA. |
| *18 Nov 2026 – 18 Feb 2027* | Advisers who solely provide payroll services. |
| *31 Dec 2026 – 31 Mar 2027* | Those already holding an ASA and financial services organisations. |
Advisers will have **three months** from the start of their registration window to apply. During that period, they can continue to act for clients while their application is under review. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Key registration requirements & conditions
To register, an adviser will generally need:
- A Government Gateway user ID and password (create one if needed)
- The adviser firm's Unique Taxpayer Reference (UTR)
- Postcode linked to that UTR
- Company & VAT registration numbers if applicable
- National Insurance number & date of birth (for sole traders, partnerships, LLPs)
- Details of anti-money laundering supervisory body where relevant. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
There are exemptions, for example where someone does not provide tax advice **as a business**, or in certain limited categories. The guidance clarifies who must register and who doesn’t. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
## Implications for businesses and clients
- **Clients** will be able to verify whether their tax adviser is registered, which offers stronger consumer protection and assurance against unqualified advice.
- **Advisers** must ensure compliance with the deadlines to avoid being unable to act for clients or risk sanctions. Non-compliance could mean being barred from dealing with HMRC on behalf of clients. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-check-if-you-need-to-register-under-new-rules?utm_source=openai))
- The digital registration process is free, replacing older systems and simplifying multiple registrations into a single process. HMRC is investing £36 million to modernise the registration infrastructure. ([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 tax advisers
1. **Check your cohort:** Use the HMRC and GOV.UK guidance to determine which registration window applies to you.
2. **Collect required information:** Ensure you have your UTR, NI number, company/VAT number, and any AML supervisory body details.
3. **Register via ASA:** Apply for or verify your Agent Services Account, if needed.
4. **Stay updated:** Guidance and secondary legislation with full definitions are being published. Ensure you follow the latest instructions.
5. **Communicate with clients:** Let clients know you are registered, and explain any new identifiers or credentials they should ask for.
## Example scenario
**Alice** is a freelance tax adviser who has been submitting Self-Assessment returns for clients but has never interacted with HMRC using Agent Services Account. She falls into Cohort 1 and must register between **18 May and 18 August 2026**. She gathers her UTR, sets up her Government Gateway ID, attaches her VAT/NI details, and submits registration. After two weeks the registration is approved. From August she can continue business as usual. If she misses the window, she risks being unable to deal with HMRC on behalf of clients until registration is completed.
## Why the change matters
By instituting MMTAR, the UK Government aims to ensure **higher professionalism**, reduce the risk of poor‐quality advice, and make it easier for taxpayers to find legitimate advisers. For advisers, compliance now ensures you can operate legitimately, maintain client trust, and avoid disruption. It’s a significant change for the tax advice market in the UK. This is essential for businesses, clients, and advisers alike.