The UK’s Mandatory Tax Adviser Registration rules: overseas advisers should check if they are in scope

In a recent edition of Tax News, we highlighted the UK’s new Mandatory Tax Adviser Registration (MTAR) rules. As this is also relevant to advisers based outside the UK, including those in Ireland who are in scope, we are sharing more details on what this means for overseas advisers and what actions need to be taken.

MTAR commenced in May in the UK and is being introduced on a phased basis with varying timeframes applying depending on the adviser type and their existing online agent account status with HMRC. The initial three-month MTAR registration period opened from 18 May 2026 for relevant in scope advisers.

The Institute’s MTAR hub provides a useful starting point for determining whether you fall within scope of the regime and identifying the registration tranche that applies to you. Members based outside the UK who did not have an HMRC online account before 18 May 2026 should urgently determine whether they fall within scope, as failure to register may prevent them from dealing with HMRC on behalf of clients. The MTAR legislation also includes various sanctions and penalties for failure to comply.

As the legislation which implements MTAR does not specifically define what an overseas adviser is, the Institute has requested clarification from HMRC on, for example, how the Northern Ireland based branch office of an Irish headquartered firm will be treated as this branch may have Irish or UK anti-money laundering (AML) supervision. AML supervision is one of the three registration criteria for those in scope. We will provide further updates as they become available.

HMRC has published detailed guidance to help advisers, including those overseas, assess whether they fall within the scope of the MTAR regime and how to register for an Agent Services Account.

HMRC has also published a new MTAR manual and is hosting stakeholder drop‑in sessions to gather feedback, identify early operational issues, and support smooth implementation. Members are encouraged to share their experiences and questions by emailing tax@charteredaccountants.ie so that these can be raised directly with HMRC.