Legislation included in the Finance Act 2026 (Part 7 and Schedules 20 and 21) requires businesses interacting with HMRC in respect of another person’s tax affairs to register as a tax adviser with HMRC. Mandatory registration with HMRC is currently in the process of being phased in, as explained in an earlier article.

General position

In general, an in-house tax team is not within scope of mandatory registration.

In its detailed guidance on mandatory registration, first published in June 2026, HMRC says that it would not expect "an in‑house tax professional or team which prepares or files tax returns solely on behalf of their employer and does not provide tax advice or services to external clients” to be required to register with HMRC (MTAR10300).

For in-house tax professionals who are interacting with HMRC on behalf of other entities within their employer’s group undertaking, the legislation provides an exemption from mandatory registration in para1(f), Schedule 20, Finance Act 2026. The term 'group undertaking' is defined by s1161(5), Companies Act 2026.

Further clarification

However, there has been concern that some types of business structures may fall outside of HMRC’s statutory exemption for corporate groups, leading to uncertainty as to whether certain in-house tax teams are required to register with HMRC.

To address these concerns, HMRC updated its guidance in August 2026 to make it clear that “registration [with HMRC] is not required where a true third-party commercial relationship does not exist" (MTAR10200). Further, HMRC says that, in most cases, where a person provides tax services to another person, and the activities "are similar in nature to those between a tax adviser and its group undertakings", the requirement to register with HMRC will not apply.

Applying the guidance 

The updated guidance includes examples of "common organisational structures" which HMRC believes fall outside of mandatory registration. These include the provision of services in joint venture and partnership arrangements and to former group undertakings post-sale.

HMRC says that, in due course, the legislation will be amended to provide statutory exemptions for the types of structure referred to in the guidance.

There is also a commitment from HMRC that it will not apply sanctions or penalties to an organisation that has concluded in error that it is not required to register, providing the organisation acted in good faith and relied on HMRC's guidance in coming to that conclusion. Instead, HMRC will "work with and support the organisation to comply with its obligation to register within a reasonable timeframe".

Implications for existing agent accounts

Over time, the criteria to register for HMRC online accounts as an agent has been tightened, including the requirement for the agent to be registered for anti-money laundering (AML) supervision. This means that, more recently, in-house teams have been unable to register for agent online services.

However, ICAEW understands that, historically, some in-house tax teams may have registered as agents in order to discuss the affairs of other group companies with HMRC. As a result, some may have an OSA, or even an ASA, allowing them to access certain tax agent services, such as corporation tax.

Under the Finance Act 2026 mandatory registration rules, an agent must apply for an ASA if they don’t already have one. At some point during this transitional phase, HMRC will check that businesses that have an OSA also have an ASA, and that businesses who have accounts (OSA and/or ASA) meet the mandatory registration requirements.

At this stage, it is not clear how HMRC will proceed where it finds that an in-house team with an OSA and/or an ASA cannot fulfil the criteria for mandatory registration (eg, proof of AML supervision, as they do not meet the requirements to be supervised). If an in-house tax team’s OSA or ASA is closed, it could lose access to the HMRC services it needs to meet the tax obligations of the entities it is responsible for.

ICAEW has raised this issue with HMRC and will keep members informed of developments.