What is the MMTAR regime?
From 18 May 2026, the UK government introduces Modernising and Mandating Tax Adviser Registration (MMTAR). Any individual or firm paid to interact with HMRC on behalf of clients must register through the streamlined digital system.(gov.uk)
Staged rollout timeline
- 18 May to 18 August 2026: new advisers or those without an Agent Services Account (ASA) interacting in Self Assessment or Corporation Tax matters.(gov.uk)
- 18 August to 18 November 2026: advisers who have SA/Corp Tax accounts but no ASA.(gov.uk)
- 18 November 2026 to 18 February 2027: payroll-only advisers.(gov.uk)
- By 31 March 2027, remaining advisers (including those with ASA, financial services entities) must be registered.(gov.uk)
What registration involves
- Applying for or ensuring you have an Agent Services Account.(gov.uk)
- Providing identity verification (NI number, DOB) if a sole trader, partner, or LLP.(gov.uk)
- Supplying any existing UTR (Unique Taxpayer Reference), VAT number, company registration number where relevant.(gov.uk)
- Registering is free, and exemption exists for those not receiving payment or not acting as professional advisers.(gov.uk)
Why it matters
- Protecting taxpayers: makes it clearer who is providing advice, enhancing accountability.(gov.uk)
- Raising standards: standardization aims to reduce poor advice in the tax market.(gov.uk)
- Market fairness: ensures all professional advisers comply with similar requirements.(gov.uk)
Who is impacted
- Any person or firm that is paid to interact with HMRC on behalf of clients about tax matters.
- Includes advisers based overseas interacting on UK taxpayer’s behalf.(gov.uk)
- Those already holding ASA do not need to re-register unless new data or conditions are required.(gov.uk)
Actionable steps
- Check if and when you must register using HMRC’s checker tools.(gov.uk)
- If not already done, set up an Agent Services Account.
- Collect needed documentation: company / VAT registrations, proof of identity.
- Understand client service obligations under registration and maintain records.
- Stay aware: different phases have deadlines; missing registration may affect ability to act for clients and potentially lead to penalties.
Example scenarios
| Situation | Do you need to register from 18 May 2026? |
|---|---|
| Newly qualified accountant offering Corporation Tax advice, no ASA yet | Yes – within first window.(gov.uk) |
| Established accountant with ASA, interacting via Self Assessment and Corporation Tax | Later windows apply; final registration must by 31 March 2027.(gov.uk) |
| Payroll specialist only dealing with payroll services | Register between November 2026 and February 2027.(gov.uk) |
By adjusting your processes now, you'll be ready for registration and able to continue representing clients without interruption.