HM Revenue and Customs has opened the second registration window under Modernising and Mandating Tax Adviser Registration (MMTAR), the programme moving tax advisers onto a single online registration route. According to HMRC, this phase applies to advisers who already have Self Assessment or Corporation Tax accounts but do not yet hold an agent services account (ASA). The deadline for this group is 18 November 2026. HMRC is advising firms to use the GOV.UK checker and submit applications early, rather than wait until the end of the window.
HMRC describes MMTAR as a free digital registration process that replaces several older ways for advisers to set up and manage their relationship with the department. To obtain an ASA, applicants must meet HMRC's published registration conditions, with the department providing step-by-step guidance through GOV.UK. The policy objective is wider than service redesign. HMRC says mandatory registration is meant to raise standards in the tax advice market, protect taxpayers and support compliant advisers, while the government says it is investing £36 million to modernise HMRC's tax adviser services.
The second window follows an initial phase that ran from 18 May 2026 to 18 August 2026 and targeted the smallest agent audience. HMRC says that first stage generated more than 4,000 applications and resulted in over 2,000 new accounts being created. Those figures show the scale of transition work already under way before larger groups are brought in. The current phase reaches advisers who are already active in Self Assessment or Corporation Tax but have not yet moved onto an ASA.
HMRC's rollout remains staggered. Advisers who solely provide professional payroll services are not required to register before 18 November 2026; their window runs from 18 November 2026 to 18 February 2027. Financial services organisations are scheduled later, with registration opening for that cohort on 31 December 2026 and running to 31 March 2027. Advisers who already hold an ASA do not need to register again. HMRC says those users will be transferred to the new digital service by 31 March 2027 and will be contacted through their account if any further information is needed.
HMRC's guidance also sets out a broad definition of who is in scope. In general, anyone paid to deal with HMRC on another person's behalf in relation to tax affairs is treated as a tax adviser unless a specific exemption applies. For firms, that means the test is practical rather than based on job title alone. Businesses need to look at the services they provide, the tax accounts they use and whether an ASA is already in place, particularly where tax work sits alongside payroll, accountancy or wider professional services.
According to HMRC, advisers can continue dealing with the department while an application is being processed, provided the application has been submitted and a registration number has been issued. The department also says access to online services will not be affected in the short term. That reduces the immediate risk of disruption, but it does not remove the need to act. HMRC is telling advisers who missed the first window, as well as new entrants to the market, to register as soon as possible so routine filing and client authorisations are not left to the final weeks.
Enforcement is part of the design. HMRC says it may restrict an adviser's ability to act for clients if registration is not completed when required, and advisers who continue to operate outside the requirement could face financial penalties. Robert Jones, HMRC's Director of Intermediaries, said the wider package is intended to strengthen trust and transparency in the tax advice market. For affected firms, the immediate compliance point is clear: confirm whether phase two applies, check HMRC's registration conditions and complete the online process before 18 November 2026 where no exemption applies.