What is MMTAR?
MMTAR stands for Modernising and Mandating Tax Adviser Registration, a policy introduced in the UK to improve accountability and raise standards among paid tax advisers. It was first announced in Budget 2025 after a public consultation in 2024.(gov.uk)
Under MMTAR, any tax adviser who is paid to interact with HMRC on behalf of clients must register via a new, centralized digital registration system. This requirement is mandatory, not optional.(gov.uk)
Timeline for rollout
The registration rollout is phased in over several periods from 18 May 2026 to 31 March 2027, targeting different groups:
- 18 May to 18 August 2026: new advisers or those without an Agent Services Account (ASA) and without a Self Assessment or Corporation Tax account.
- 18 August to 18 November 2026: advisers with Self Assessment or Corporation Tax accounts but no ASA.
- 18 November 2026 to 18 February 2027: advisers only offering payroll services.
- 31 December 2026 to 31 March 2027: final group to be phased in.(gov.uk)
Who is affected and what’s required
- If you are paid to act for clients before HMRC—filing returns, engaging on self assessment, corp tax, etc—you’re a tax adviser and must register, unless exempt.
- Also applies to overseas advisors dealing with UK taxpayers.
- Registration requires various identifiers and personal information like UTR, ASA credentials, government gateway ID, VAT number, NI number, AML supervisory body info (if applicable) and verification of identity.(gov.uk)
Goals and implications
- Protecting consumers: Clients will have clearer recourse and can easily verify registered advisers.
- Raising standards: Consistent expectations around conduct and accountability.
- Transparency and compliance costs: Advisers must plan for administrative work to register and maintain compliance.
Action items for personnel
- Determine whether you fall under the definition of “tax adviser” under MMTAR—if you get paid and interact with HMRC for clients. If not, you may be exempt.
- Prepare required documentation ahead of your phase’s registration window. Missing deadlines may risk non-compliance.
- Overseas service providers should ensure systems are in place to comply.
The MMTAR rollout represents a significant shift in the UK tax advisory landscape. Those who understand the requirements early will help avoid compliance pitfalls and better serve clients.