How to request specific HMRC agent authorisation codes

To act on behalf of your clients, you must obtain unique agent codes for each specific tax regime—such as Self Assessment, VAT, or Corporation Tax—from HMRC. These codes act as your professional ID, allowing your tax software to "talk" to HMRC and securely link your business to your clients’ tax records so you can file returns on their behalf.

Why do you need specific codes?

In the UK, HMRC treats different types of tax as separate "regimes." Even if you have a main Agent Services Account (ASA), legacy systems for Self Assessment and Corporation Tax often require their own distinct agent codes. You will need to input these codes into your chosen tax software to authorise it to submit data. Without them, you are essentially "locked out" of your clients' records, even if the client has signed a paper mandate.

How to request your agent codes

1. Log in to your HMRC account: Use your Government Gateway credentials to log into your 'HMRC Online Services for Agents'. Note that this may be different from the newer 'Agent Services Account' used for Making Tax Digital (MTD).
2. Navigate to 'Services you can add': Once logged in, look for the option to add a new tax service or "Request an agent code."
3. Select the Tax Regime: You will need to apply for codes individually. Common ones include:
   • Self Assessment: For individual tax returns and sole traders.
   • Corporation Tax: For limited company tax returns.
   • PAYE for Agents: If you are managing payroll for clients.
4. Verify your details: HMRC will ask you to confirm your business details, such as your firm’s name, address, and your own Unique Taxpayer Reference (UTR).
5. Receive your code: For security, HMRC often sends these codes via post to your registered business address. This can take up to 10–14 days, so it is vital to do this well before your first filing deadline.

The difference between codes and "The Handshake"

It is important to distinguish between your Agent Code and Client Authorisation. The Agent Code identifies you to HMRC’s system. Once you have the code and have entered it into your software, you still need to link individual clients to your account. For modern services like VAT, this is often done via a "digital handshake" (an email link the client clicks), whereas for older systems, you may still need to use the codes to generate an authorisation request by post.

Top Tip: Keep a secure record of every agent code you receive. You will only need to enter them into your tax software once during the initial setup, but having them on hand will save you a headache if you ever switch software providers or need to contact HMRC's agent dedicated helplines.

What to do next

Once your codes arrive in the post, log back into your software and enter them into the "Agent Settings" or "HMRC Credentials" section. This effectively "unlocks" those tax regimes within your software, allowing you to begin the process of onboarding and linking your clients.