Compliance
Tax Adviser Registration Mandates: What Advisers Need to Do under MMTAR
Tax advisers must comply with new registration rules introduced under MMTAR, ensuring proper authorisation and access to HMRC services by August 2026 and through into 2027, or risk disruption to their practice.
By NomadicTax Research Team • 5 min read • September 7, 2026
## What is MMTAR?
Modernising and Mandating Tax Adviser Registration (MMTAR) is HMRC’s initiative to ensure that anyone **paid to interact with HMRC on behalf of someone else about their tax affairs** must be registered as a tax adviser—unless exempt. This is to protect taxpayers, raise standards, and improve oversight. ([gov.uk](https://www.gov.uk/government/news/tax-advisers-one-month-left-to-register-under-new-rules?utm_source=openai))
## Key Dates & Phases
| Phase | Who it affects | Deadline |
|-------|------------------|----------|
| Phase 1 | New tax advisers or those without an Agent Services Account, SA or Corporation Tax account | **18 August 2026** ([gov.uk](https://www.gov.uk/government/news/tax-advisers-one-month-left-to-register-under-new-rules?utm_source=openai)) |
| Phase 2 | Advisers with a Self Assessment or Corporation Tax account but without an Agent Services Account | 18 November 2026 |
| Phase 3 | Advisers who solely provide payroll services | 18 February 2027 |
| Phase 4 | Those who already have an ASA; financial services organisations | 31 December 2026 to 31 March 2027 |
## Why It Matters for Advisers
- **Access to HMRC services**: Without registration, you may lose ability to interact with HMRC digitally on behalf of clients.
- **Reputation & compliance**: Being properly mandated adds legitimacy and aligns with regulatory expectations.
- **Risk of penalties or operational disruptions**: Unregistered advisers may find some engagements invalid or refused by HMRC.
## Action Steps for Advisers
1. **Check whether you must register**: If you interact with HMRC for clients (SA, CT, PAYE, etc.), and do not yet have an ASA or proper formal registration, you likely need to act now.
2. **Apply for Agent Services Account (ASA)**: It’s central to registration. Ensure you have one if you act for clients.
3. **Register under MMTAR**: Use HMRC’s new registration process. Complete identification and verification procedures as required.
4. **Train your practice**: Understand the phases, deadlines, and which services you’ll be required to use or lose access to.
5. **Inform your clients**: Clients should know you are registered under MMTAR—it instills confidence they’re working with someone recognised by HMRC.
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## Case Examples
a) **Small accounting firm without ASA**: All staff interacting with HMRC must ensure individual or firm registration by 18 August 2026 under Phase 1.
b) **Payroll-only provider**: Even if you only do payroll, you’re explicitly included in later phases (Phase 3) with deadline 18 February 2027.
c) **Financial services organisations**: Registration likely occurs in final phase (Dec 2026–March 2027); important for compliance with regulations across sectors.
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## Potential Challenges
- **Delays in verification**: Some may experience delays in identity checks or ASA setup—apply early.
- **Software or digital access issues**: Costs to upgrade or adapt systems may be needed.
- **Client communication**: Some clients may expect advisers to be registered already; failure to comply could damage trust.
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## Bottom Line for Advisers
MMTAR is not optional for professionals who engage with HMRC on their clients’ behalf. Understand which phase applies, register promptly, maintain correct ASA status, and ensure your practice is prepared for audits of adviser registration. Being ahead of these rules will avoid disruption, reputational risk, and lost business opportunities.