The Tax Agent Process

Working as a Tax Agent: what you need to know (2026 Update)

1. Important: Mandatory Tax Adviser Registration

From 18 May 2026, HMRC has introduced a new legal requirement for all tax advisers. To interact with HMRC on behalf of clients, you must be formally registered and meet "minimum standards" (no outstanding tax returns or payments of your own, no criminal record, and active AML supervision).

• Existing Agents: If you already have an Agent Services Account (ASA), you will be migrated to the new register automatically, though HMRC may contact you to verify your details.

• New Agents or Agents with an Agent Online Services Account (AOSA) only: You must register between 18 May and 18 August 2026. Failure to register may result in financial penalties or being blocked from representing clients.

>> Find out more about Registering as a Tax Adviser

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2. Security & Credentials: The "Golden Rule"

You must always use your own agent credentials to log in.

Warning: You must never use a client's personal Government Gateway credentials or log in as a "team member" of the client’s own account. This misrepresents the relationship to HMRC, bypasses the "Standard for Agents" protections, and can be seen as a breach of AML regulations. All work must be performed through your own Agent Online Services Account (AOSA) or Agent Services Account (ASA).

GOV.UK One Login

HMRC is transitioning from the old Government Gateway to GOV.UK One Login.

• New Agents (from Feb 2026): You will likely be prompted to create a GOV.UK One Login using an email, password, and identity verification (e.g., passport/driving licence).

• Existing Agents: Continue using your 12-digit Government Gateway ID until HMRC contacts you to migrate your account to One Login.

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3. Qualifying via ICB & AML Supervision

To practise as a tax agent under the ICB umbrella, you must hold a valid ICB Practice Licence or AML Supervision Licence (for non-member practices).

Anti-Money Laundering (AML)

By law, you cannot act as a tax agent without AML supervision. Your ICB Licence provides this.

• Registration Prompt: When HMRC asks for your AML supervisor, select "Institute of Certified Bookkeepers (ICB)".

• Reference Number: When prompted for your registration number, enter your ICB Licence Number.

Required Qualifications

To comply with ICB's Professional Conduct Regulations you must be qualified in the specific tax area you offer:

• VAT: MICB status (Member) or above.
• PAYE: Payroll Agent or PM Dip (Payroll Diploma).
• Self-Assessment: Level 4 Diploma in Self-Assessment (or its now discontinued predecessor Level 3 Certificate)
• Corporation Tax: Level 4 Diploma in Financial Statements AND Corporation Tax.

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4. Understanding Your Two HMRC Accounts

HMRC uses two parallel systems. You may need both.

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5. Obtaining Codes & Authorisation for MTD for Income Tax (MTD IT)

The process for MTD IT differs from legacy services. You do not get a specific "MTD Agent Code." Instead, you use your Agent Services Account (ASA).

Step 1: Link Your Existing Legacy Codes

If you already have a Self-Assessment Agent Code and authorised clients in your AOSA, you must "link" them to your ASA.

• Log into your ASA.
• Select "Allow this account to access existing client relationships."
• Enter your legacy Government Gateway credentials and your Self-Assessment Agent Code.
• This "maps" your existing authorisations across so you can act for those clients in MTD IT without needing a new digital handshake.

Step 2: For New Clients (The Digital Handshake)

If you do not have an existing legacy authorisation for a client, you must use the ASA to create a new authorisation:

1. Log into your ASA.
2. Select "Ask a client to authorise you."
3. Choose the Role: You will be prompted to choose between being a Main Agent or a Supporting Agent.
4. The system generates a unique URL link.
5. Email this link to your client. They must log in to their own account to approve you.

Step 3: Mandatory Sign-Up (The Final Step)

Authorisation is not the same as Registration. Once you are authorised:

• You must manually sign up each client for MTD IT via the ASA.
• Once signed up, you then link your MTD-compatible software to your ASA to begin quarterly submissions and/or end-of-year-tax.
  
  

> Get further ICB Guidance about MTD

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6. Obtaining Legacy Tax Agent Codes (AOSA)

For services not yet on the ASA, you still need individual "Head of Duty" codes for your AOSA:

• Self-Assessment (Classic) & Corporation Tax: If you don't have an AOSA, you must apply in writing to: Agent Compliance Team, HMRC, BX9 2BG.
• PAYE & CIS: These can be requested online through your AOSA and are usually issued immediately.
• VAT: You use your own VAT Registration Number or apply for a VAT Agent Reference Number via your ASA.

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7. Managing Changes Your Practice

Adding Team Members (Staff)

You should not share your admin login with staff. Instead:

• In the ASA: Go to "Manage account" and then "Add a user."
• In the AOSA: Use the "Manage users" link.

Changing your details

If your practice moves address, changes names, or changes legal entity, you must inform HMRC and ICB straight away.

a. Changing Your Legal Entity (e.g., Sole Trader to Ltd)

This is a material change and is treated as the end of one business and the start of another.

• HMRC: You must re-register for a new Agent Services Account and a new Tax Adviser Registration.
• ICB: You must notify ICB within 14 days. You are required to transfer to a new Practice Licence.

b. Where and How to Update HMRC

• Agent Services Account (ASA): Log in and use the "Manage account" section.
• Agent Online Services (AOSA): Update your legacy contact details via the "Your account" section.
• If changing your Business Name (but not legal entity), write to the Agent Maintainer Team at BX9 2BG.

c. The ICB "Material Change" Rule

As an ICB member, you must report changes within 14 days, including legal entity, MLRO changes, new BOOMs, or changes in trading address.

Pro Tip: Update ICB first. If details given to HMRC don't match ICB's records, your registration update may be rejected.

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