Legislation included in the Finance Bill 2025-26 requires businesses interacting with HMRC in respect of another person’s tax affairs to register with HMRC.  

HMRC has now published initial guidance on GOV.UK explaining: 

• how to check if you need to register as a tax adviser; and
• if and how to register as a tax adviser.  

The guidance states that where an adviser is required to register with HMRC, they will need an ASA if they do not already have one.  

Caution required 

The guidance is helpful as it provides an introduction to, and overview of the rules, including who is and is not in scope. However, ICAEW recommends that tax advisers treat the guidance with caution as it oversimplifies the legislation and leaves some questions unanswered. 

In particular, ICAEW is concerned that the GOV.UK guidance: 

• does not fully explain when agents require an ASA. ICAEW assumes that all tax agents will need to apply for an ASA even if they are applying to be registered with HMRC as an agent for a HMRC service that does not currently require an ASA (eg, for services where only a Government Gateway user ID is required such as Stamp Taxes). However, this is not clear from the guidance; 
• inaccurately describes who is a ‘relevant individual’, which is a key requirement for registration;
• does not give enough detail in some areas, for example, on how to determine if a person is an “officer” of the business for the purposes of agent registration; and
• does not provide the clarity that a lot of tax agents are seeking, for example, on whether family offices need to register and if registration is at an entity or a group level. 

ICAEW understands that HMRC intends to publish more information in due course. In the meantime, tax agents should read the GOV.UK guidance alongside the Finance Bill legislation: 

• clause 220-246 (framework for agent registration); 
• Schedule 20 (exceptions from the requirement to register); and
• Schedule 21 (reviews and appeals).  

Timetable for registration 

HMRC is currently in the process of building an online service that tax agents can use to register with HMRC.   

The GOV.UK guidance confirms that agents will be required to use the service to register from 18 May 2026 unless: 

• they already have an ASA. HMRC says that advisers with an ASA “will not need to register again”. However, HMRC will contact the adviser through their ASA to collect any information needed to check that they meet the conditions for agent registration. It is not clear when HMRC will begin contacting agents with an existing ASA; 
• they do not have an ASA but do have a self assessment and/or corporation tax account (ie, an online service account). In this case, the adviser may register from 18 May 2026 and must register from 18 August 2026; or
• they only provide third-party payroll services on behalf of clients and do not interact with HMRC in any other way, in which case they may register from 18 May 2026 and must register from 18 November 2026.  

ICAEW's view

The adviser will have three months from the date they need to register to apply for an ASA. They can continue to interact with HMRC on behalf of their clients during those three months while HMRC considers their registration.