What is MMTAR?
Modernising and Mandating Tax Adviser Registration (MMTAR) is a government programme created to bring consistent standards and transparency to the tax advice market. All advisers paid to manage or liaise with HMRC on behalf of clients must register under this scheme. (gov.uk)
When and How Phases Roll Out
Registration is being introduced in stages, to different categories of tax advisers:
| Phase | Adviser Type | Registration Opens |
|---|---|---|
| Phase 1 | New advisers, or those dealing with HMRC without an Agent Services Account or Self Assessment/Corporation Tax account | 18 May–18 August 2026 (gov.uk) |
| Phase 2 | Advisers with Self Assessment or Corporation Tax accounts, but without ASA | 18 August–18 November 2026 |
| Phase 3 | Payroll-only service providers | 18 November 2026–18 February 2027 |
| Phase 4 | Remaining advisers to complete transition | by 31 March 2027 |
Registration is free, done online, and will require verifying identity and possibly Anti-Money Laundering (AML) supervisory body details. (gov.uk)
Key Requirements & Obligations
- Must hold an Agent Services Account (ASA) to interact with HMRC on clients’ behalf.
- Provide your UTR, company registration number if applicable, VAT number if registered, National Insurance, date of birth.
- Maintain required AML supervisory body membership where needed.
- Registration applies to overseas advisers who act for UK taxpayers. Exemptions exist for volunteers not in business, or certain non-paid roles. (gov.uk)
Consequences of Not Registering
- Loss of access to HMRC services for unregistered agents
- Advice could be treated as invalid in tax proceedings
- Potential penalties or professional sanctions for facilitating incorrect claims or evasion—part of wider powers introduced by HMRC in 2026 (gov.uk)
Example
Consider “Bright Tax Consulting,” a small firm offering payroll services only. They must register between 18 November 2026 and 18 February 2027, under Phase 3, even if already registered for other services. Missing that deadline bars them from interacting with HMRC as agents thereafter.
Tips to Prepare Early
- Check if you’re already registered or qualify for exemption now
- Gather required documents in advance—UTR, company number, etc.
- Ensure membership in AML supervisory bodies if needed
- Ensure software/hardware meets secure standards
Takeaway: If you act as a paid tax adviser interacting with HMRC—no matter your size or speciality—you’ll need to register under MMTAR according to your phase. Delay can cost your firm access and credibility.