HMRC Opens Phase 2 Tax Adviser Registration: 18 November 2026 Deadline for Self Assessment and Corporation Tax Agents

HMRC has opened the second phase of mandatory tax adviser registration, requiring eligible advisers to register by 18 November 2026^[1]. The move targets tax advisers with Self Assessment or Corporation Tax accounts who do not yet hold an agent services account (ASA), extending the Modernising and Mandating Tax Adviser Registration (MMTAR) programme to a broader segment of the UK advisory sector.

Phase Two Eligibility and Timeline

According to HMRC^[1], registration is now open for advisers with Self Assessment or Corporation Tax accounts but without an ASA. The 18 November 2026 deadline applies specifically to this cohort. Advisers who solely provide professional payroll services do not need to register before 18 November, while financial services organisations have until 31 December 2026^[1].

HMRC is encouraging advisers in the second registration window to check eligibility and submit applications as soon as possible^[1]. The registration process is free and online, with step-by-step guidance and an interactive checker tool available on GOV.UK^[1].

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."^[1]

First Phase Compliance Benchmark

More than 4,000 applications were submitted and over 2,000 accounts created during the first registration window, which targeted the smallest agent audience group^[1]. This provides a baseline for phase two compliance expectations, though HMRC has not disclosed the total number of eligible advisers in either phase.

The mandatory changes are designed to raise standards in the tax advice market, protect taxpayers, and support those who play by the rules^[1]. MMTAR is a single, streamlined digital registration system that replaces a range of previous processes, making it easier for tax advisers to interact with HMRC^[1].

Registration Requirements and Conditions

Eligible tax advisers must meet HMRC's registration conditions to apply for an ASA^[1]. While HMRC has not published the full list of conditions in the 18 August announcement, the registration system is intended to create a unified framework for tax advisory services across Self Assessment, Corporation Tax, and other tax regimes.

The phased rollout reflects HMRC's approach to implementing mandatory registration across different adviser populations, starting with smaller groups before extending to larger cohorts. Phase two's focus on Self Assessment and Corporation Tax accounts suggests a significant expansion of the registration requirement compared to the initial phase.

UK Register Context: Advisory Sector Landscape

Across the UK company register, 33,984,851 active officers are recorded, with a further 3,819,262 resigned officers^[2]. These economy-wide totals encompass all officer roles across all sectors, providing context for the scale of the UK business population within which tax advisers operate.

Daily incorporation activity across the UK register shows sustained business formation, with 2,888 companies incorporated on 18 August 2026 - the day HMRC opened phase two registration^[2]. In the preceding 30 days, daily incorporations ranged from 328 to 3,334 companies^[2]. These figures reflect the entire UK register, not advisory sector activity specifically.

London hosts 1,030,267 registered companies across all sectors, followed by Manchester (100,484), Birmingham (90,212), Glasgow (69,449), and Edinburgh (57,265)^[2]. The distribution of registered companies by locality provides a proxy for where tax advisory services are likely to be concentrated, though individual tax advisers may operate as sole traders or unincorporated partnerships not captured in these company-level statistics.

As of the latest data, the UK register contains 5,568,202 active companies from a total of 6,595,284 registered entities^[2]. Incorporations in the past seven days totalled 13,889 across all sectors^[2].

Forward Compliance Risk

The 18 November 2026 deadline creates a 13-week window for phase two compliance. HMRC has not published estimates of how many advisers fall within phase two eligibility, making it difficult to project total application volumes or identify non-compliance risk at a sector level.

The absence of sector-specific registration data means advisory firms, accountancy practices, and sole trader tax agents cannot yet benchmark their compliance status against peer groups or regional cohorts. CompanyPulse users can filter the UK register by officer roles and company names to identify potential advisory businesses, but this does not capture unincorporated advisers or distinguish between registered and unregistered MMTAR participants.

Phase two's broader scope - covering Self Assessment and Corporation Tax accounts - suggests a larger eligible population than phase one's 4,000 applications^[1]. Whether compliance rates will match or exceed the first window's conversion from applications to active accounts remains an open question as the November deadline approaches.