Mandatory Tax Adviser Registration

HMRC Publishes Long Awaited Guidance on Mandatory Tax Adviser Registration

On 1 June 2026, HMRC published detailed guidance in its internal manuals on the new Mandatory Tax Adviser Registration (MTAR) regime. While the legislation itself was enacted through the Finance Act 2026, the guidance provides the clearest indication yet of how HMRC intends to operate the regime in practice and who will be affected.

The message from HMRC is clear: this is not simply a registration exercise. It is the creation of an ongoing regulatory framework for businesses that interact with HMRC on behalf of clients.

A wider net than many advisers may expect

Under the new rules, businesses must register if they interact with HMRC in relation to another person’s tax affairs and are paid for providing that service.

Importantly, HMRC’s definition of a tax adviser is deliberately broad. It extends beyond traditional tax advisory firms to include anyone assisting clients with their tax affairs where that assistance involves interaction with HMRC.

As a result, the regime may apply to accountants, tax agents, payroll providers, financial advisers, wealth managers, conveyancers and even some in-house tax functions operating within corporate groups.

HMRC repeatedly emphasises throughout the guidance that businesses should focus on what they actually do, rather than how they describe themselves. A firm may find itself within scope even if tax advice forms only a small part of its wider service offering.

Conveyancers and payroll providers should pay particular attention

The guidance contains detailed examples for sectors that may not immediately think of themselves as tax advisers.

For conveyancers, activities such as submitting Stamp Duty Land Tax (SDLT) returns, making SDLT payments, or corresponding with HMRC about a client’s SDLT position are all likely to trigger registration requirements.

Similarly, payroll providers that submit RTI returns, PAYE returns or PAYE payments to HMRC on behalf of clients are likely to be caught by the regime. Businesses that simply provide payroll software, payroll calculations or administrative support without interacting with HMRC will generally remain outside scope.

Registration is only the beginning

One of the most significant developments in the guidance is the detail HMRC has provided on the conditions businesses must satisfy to obtain and maintain registration.

Following an application for an Agent Services Account (ASA), HMRC will assess whether the business and certain senior individuals connected with it meet a series of registration conditions.

To qualify, a business must not have:

• Outstanding tax returns or unpaid tax liabilities (unless covered by an agreed Time to Pay arrangement);
• Relevant unspent convictions for tax or fraud offences;
• Director disqualifications;
• Insolvency proceedings;
• Anti-avoidance sanctions or stop notices; or
• A history of being refused dealings with HMRC.

Businesses must also demonstrate that they are subject to appropriate anti-money laundering (AML) supervision before registration can be completed.

For new firms, this could be particularly important. HMRC has made clear that simply applying for AML supervision will not be sufficient; approval must already be in place before registration can be granted.

HMRC’s spotlight on “relevant individuals”

Perhaps the most notable feature of the new regime is HMRC’s focus on what it calls “relevant individuals”.

These are not ordinary employees who happen to deal with HMRC on a day-to-day basis. Instead, they are the individuals who exercise significant strategic or managerial control over a firm’s tax advisory activities.

Depending on the size and structure of the business, relevant individuals may include:

• Heads of Tax;
• Tax practice leaders;
• Senior partners or directors responsible for tax services;
• Individuals who determine how tax services are managed, governed or controlled.

HMRC will carry out checks on these individuals, including identity verification, criminality checks, insolvency checks and reviews of their personal tax compliance.

For smaller firms, the rules are particularly straightforward. Where there are fewer than six partners, directors or equivalent officers, all of them will generally be treated as relevant individuals for registration purposes.

An ongoing compliance regime

The guidance also confirms that registration will not be a one-off event.

HMRC intends to carry out ongoing monitoring of registered businesses and relevant individuals through periodic compliance checks and risk-based reviews.

Registered firms will be expected to continue meeting the registration conditions and to comply with HMRC’s Standard for Agents. HMRC stresses that responsibility for compliance sits with the business as a whole, rather than individual relevant individuals personally overseeing every client interaction.

Businesses will also be expected to notify HMRC of changes to relevant individuals from April 2027 onwards.

Registration timetable already underway

The registration process is being introduced in stages between May 2026 and March 2027.

The first registration window opened on 18 May 2026 for new advisers and businesses that interact with HMRC without an Agent Services Account. Further tranches will follow for advisers with existing HMRC credentials, payroll-only providers and financial services organisations.

Existing holders of an ASA will not need to apply again, but HMRC will contact them during the transition period to obtain additional information and assess compliance against the new standards.

What should businesses do now?

The publication of HMRC’s guidance provides a much clearer picture of how the registration regime will operate. However, it also highlights that many businesses may be affected despite not viewing themselves as tax advisers.

Firms should begin by assessing whether any part of their business interacts with HMRC on behalf of clients. If it does, they should then consider whether they meet HMRC’s registration conditions, whether their AML supervision arrangements are in place, and who within the organisation may be regarded as a relevant individual.

The new regime is ultimately about more than registration. It is about demonstrating ongoing compliance, maintaining professional standards and satisfying HMRC that those interacting with the tax system on behalf of others meet a defined set of suitability requirements.