HM Revenue and Customs (HMRC) has issued a new warning to tax advisers as the second phase of mandatory registration rules gets underway. Advisers with Self Assessment or Corporation Tax accounts who do not already have an agent services account (ASA) have until November 18, 2026 to register.
HMRC is urging those affected to check whether they need to register and submit an application as soon as possible.
MMTAR Programme and Registration Windows
The new requirements are part of the Modernising and Mandating Tax Adviser Registration (MMTAR) programme, which is being introduced in phases and is designed to raise standards in the tax advice market and provide greater protection for taxpayers.
More than 4,000 applications were submitted during the first registration window and over 2,000 accounts were created. Registration is free and can be completed online through GOV.UK.
Robert Jones, HMRC’s Director of Intermediaries, said: “Together, these measures will reinforce trust and transparency across the tax advice market, supporting high standards and helping taxpayers access advice with greater confidence.”
“Now that the second registration phase is open, advisers in the next group should check the guidance on GOV.UK and make sure they register by 18 November 2026.”
Who Needs to Register
Anyone who is paid to interact with HMRC on behalf of someone else about their tax affairs is generally considered to be a tax adviser, unless an exemption applies. The current registration window, running from August 18 until November 18, applies to advisers with a Self Assessment or Corporation Tax account who do not have an ASA.
Tax advisers who already have an ASA do not need to register again. They will be moved to the new digital service by March 31, 2027, with HMRC contacting them directly if any additional information is required.
Advisers who solely provide professional payroll services do not need to register during the current window. Their registration period will run from November 18, 2026 until February 18, 2027. Financial services organisations will have a separate window running from December 31, 2026 until March 31, 2027.
Consequences of Non-Compliance
Advisers who missed the first registration window, which closed on August 18, or who are new to the tax advice market have been urged to register as soon as possible. HMRC said advisers who have submitted an application and received a registration number can continue to deal with the department on behalf of their clients while their registration is being processed.
Access to HMRC online services will also not be affected in the short term. However, HMRC warned that it may limit an adviser’s ability to act on behalf of clients if they fail to register when required. Advisers who continue to operate without completing the mandatory registration could also face enforcement action, including financial penalties. The UK Government is investing £36 million to modernise HMRC’s tax adviser services.
