HMRC Opens Next Mandatory Tax Adviser Registration Window as AML Supervision Checks Continue

HM Revenue & Customs has moved into the next phase of the UK’s mandatory tax adviser registration regime, with a new three-month registration window opening on 18 August 2026 for advisers who already have a Self Assessment or Corporation Tax agent account but do not yet have an Agent Services Account (ASA).

The change forms part of HMRC’s Modernising and Mandating Tax Adviser Registration programme. Under the phased timetable, the first window ran from 18 May to 18 August 2026 for new tax advisers and advisers interacting with HMRC without an ASA, Self Assessment or Corporation Tax account. The second window now runs from 18 August to 18 November 2026. Advisers who solely provide third-party payroll services follow from 18 November 2026, while certain financial services organisations enter their registration window from 31 December 2026.

AML supervision is part of the registration conditions

The regime applies broadly to businesses that are paid to interact with HMRC on behalf of clients about their tax affairs, unless a specific exemption applies. Businesses have three months from the start of their applicable window to register and may continue interacting with HMRC during that period and while an application submitted on time is being processed.

HMRC’s registration conditions include checks intended to raise standards in the tax advice market. Businesses may be required to demonstrate that they are appropriately supervised for anti-money laundering purposes, including identifying their AML supervisory body and providing relevant membership or registration details. HMRC guidance also states that the business and specified relevant individuals must continue to meet the applicable registration conditions after registration.

The requirement also extends to overseas tax advisers who interact with HMRC on behalf of UK taxpayers, although HMRC uses a different registration route for overseas businesses. Where supporting evidence is required, overseas advisers may need authenticated documentation, including notarised and, where necessary, translated records.

Failure to register can disrupt client work

HMRC states that advisers who are required to register but fail to do so will not be able to interact with HMRC on behalf of clients and may face sanctions if they continue attempting to act without registration.

The 18 August milestone is therefore more than an administrative date. It extends a formal gatekeeping framework in which access to HMRC client-facing services is increasingly tied to adviser registration, fitness conditions and evidence of AML supervision.