Second HMRC registration window now open for tax advisers

The second registration window for HMRC’s Modernising and Mandating Tax Adviser Registration (MMTAR) scheme opened on 18 August and applies to tax advisers who have a Self Assessment or Corporation Tax agent account but do NOT have an Agent Services Account (ASA). Advisers within this group must register by 18 November 2026.

HMRC introduced MMTAR in May 2026 as a new, single digital registration system for tax advisers. The changes are intended to provide greater oversight of the tax advice market, support professional standards and protect taxpayers, while replacing a number of existing registration processes.

Anyone who is paid to interact with HMRC on behalf of another person in relation to their tax affairs is generally considered to be a tax adviser, unless an exemption applies. The first phase of registration which covered unregistered tax advisers closed on 18 August 2026.

There are two further phases. The first covers tax advisers who solely provide professional payroll services, with registration open from 18 November 2026 to 18 February 2027. The second covers financial services organisations, which are required to register between 31 December 2026 and 31 March 2027.

If you are unsure whether you need to register, HMRC has published guidance and an interactive checker to help advisers determine whether they are required to register, what information they need to provide and when they need to register. There is also a handy ATT FAQ webpage.

Advisers who submit an application and receive a registration number can continue to interact with HMRC while their application is being processed. However, HMRC has warned that it may restrict an adviser’s ability to act on behalf of clients where they fail to register when required. Enforcement action, including sanctions and financial penalties, may also apply, and HMRC have recently updated their guidance manual on  guidance manual on sanctions and safeguards

Those who are affected by the second phase should therefore make sure they understand the new requirements and complete their registration before 18 November 2026.