HMRC has announced a mandatory tax adviser registration requirement under the Modernising and Mandating Tax Adviser Registration (MMTAR) framework, with phased implementation beginning on 18 May 2026 and running through to 31 March 2027. Registration will be free and supported by GOV.UK guidance.
UK’s HM Revenue and Customs (HMRC) has announced the introduction of a mandatory registration requirement for tax advisers, with implementation beginning on 18 May 2026.
The new requirement, known as Modernising and Mandating Tax Adviser Registration (MMTAR), was first announced at Budget 2025 following public consultation in 2024. Consultation responses were strongly in favour of introducing registration, aimed at improving adviser identification, ensuring consistent standards, and strengthening taxpayer protection.
HMRC confirmed that online registration will be introduced in phases between 18 May 2026 and 31 March 2027. Registration will be free, and guidance will be available on GOV.UK to support advisers through the process.
The government is investing GBP 36 million to support HMRC’s modernisation of the registration system, as part of its Plan for Growth. GOV.UK guidance on MMTAR was published on 17 February 2026, setting out that eligible tax advisers must meet HMRC’s registration conditions to apply for an agent services account (ASA).
A tax adviser is defined as any person who interacts with HMRC on another person’s tax affairs and is paid to do so. The requirement applies to advisers and agents both in the UK and overseas, unless an exemption applies.
HMRC Director for Intermediaries Robert Jones said:
“Tax advisers are encouraged to check the guidance now, to understand if and when they need to register, and prepare ahead of their registration window. We are taking action to raise standards in the tax advice market, support economic growth and help close the tax gap.
These new registration requirements will create a fairer market for taxpayers, help them get more reliable advice, and support the majority of advisers who play by the rules.”
Phased registration timetable
HMRC will introduce the requirement gradually:
- 18 May to 18 August 2026: New tax advisers, or advisers interacting with HMRC without an ASA, Self Assessment or Corporation Tax account.
- 18 August to 18 November 2026: Advisers with a Self Assessment or Corporation Tax account, but without an ASA.
- 18 November 2026 to 18 February 2027: Advisers who solely provide payroll services.
- 31 December 2026 to 31 March 2027: Advisers who already have an ASA, and Financial services organisations (final definition to be set out in secondary legislation).
Advisers will have three months from the start of their assigned registration window to apply for an ASA. During this period, and while HMRC processes applications, advisers may continue to interact with HMRC on behalf of clients.
If an adviser already holds an ASA, re-registration will not be required. HMRC will contact existing ASA holders if further information is needed for migration to the new digital system.
Compliance and enforcement
HMRC has stated that advisers who fail to register by the relevant deadline, or who do not meet the required standards, will not be permitted to interact with HMRC on behalf of clients. Continued non-compliance may result in sanctions, including financial penalties where advisers continue to act after being instructed to stop.
Failure to register may also result in disruption to client services and damage to trust in professional tax advice.
Registration requirements and exemptions
To register, advisers will be required to provide details including Government Gateway credentials, Unique Taxpayer Reference (UTR), company registration number where applicable, VAT registration number where applicable, and personal identification details for sole traders and partnerships. Information relating to anti-money laundering supervision will also be required.
Exemptions will apply in specific cases, including certain activities such as customs intermediation, and where individuals or organisations do not provide tax advice as a business, such as some voluntary sector bodies.
HMRC has also published stakeholder materials to support implementation of the MMTAR process, alongside GOV.UK guidance outlining who is required to register and who is exempt.
The department stated that the reforms are intended to support a more consistent, secure and transparent framework for tax advisers interacting with HMRC in future.
