HMRC does not give an agent firm one number. The agent services account has its own agent reference number, the older HMRC online services for agents account holds separate agent codes for Self Assessment and Corporation Tax, PAYE and CIS rely on a PAYE agent ID code and an agent Government Gateway identifier, and several smaller services issue their own references. Knowing which identifier belongs where avoids rejected authorisations, misdirected repayments and clients who never appear on the firm’s lists.
Why does HMRC use so many agent identifiers?
Because agents work through two separate systems. HMRC’s guidance on registering as a tax agent says services may be reached through an agent services account, through an HMRC online services account, or by signing in directly with an agent Government Gateway user ID. Its Making Tax Digital guidance is blunt that the agent services account is different from the HMRC online services for agents account. Each system has its own sign in details and its own identifiers, and a firm that has traded for some years will usually hold both.
Registration is also changing. HMRC now treats anyone paid to deal with it on someone else’s tax affairs as a tax adviser who must register by applying for an agent services account. The requirement is being phased in: according to HMRC, firms that already have a Self Assessment or Corporation Tax account must register from 18 August 2026, businesses that only provide third party payroll services from 18 November 2026, and financial services organisations from 31 December 2026, each with three months from the opening of their window. HMRC’s online checker asks whether the business has previously registered for a Self Assessment or Corporation Tax agent code, which shows how central those older codes still are. Our guide to the agent services account covers the registration conditions.
What is the agent reference number?
The agent reference number, often shortened to ARN, is issued once the firm has created its agent services account. It belongs to the account through which the firm sends digital handshake requests for client authorisation, the route HMRC uses for Making Tax Digital for Income Tax, VAT and other newer services. HMRC’s guidance on the handshake stresses that it must be sent using the agent services account sign in details, not the details used for HMRC online services.
The ARN also appears on paper. A paid agent who wants repayments from P87, R40 or Marriage Allowance claims paid to the firm must give its agent reference number in the nomination section, and the name and address on the form must match the agent services account. See nominating repayments to an agent for the signature rules that go with it.
What are Self Assessment and Corporation Tax agent codes?
These codes belong to the HMRC online services for agents account. HMRC’s guidance on form 64 8 describes the Self Assessment agent code as six characters in the format 1111XX, and asks that only that code is entered in the Agent code (SA) box. The form has a separate Agent code (CT) box for Corporation Tax. To use the Self Assessment for Agents service, HMRC says a firm needs an agent code, registration with HMRC online services, the service added to its portfolio and an authorisation for each client, and that it must register for the service even if it files with commercial software.
Self Assessment agent codes now also bridge into the agent services account. Before signing clients up for Making Tax Digital for Income Tax, a firm can add a Self Assessment agent code to its agent services account, which brings across every client authorisation linked to that code and treats the firm as main agent. The account then shows a list of codes added, not individual clients, and a firm with more than one code repeats the process for each. Adding a code links the two accounts, so later changes to Self Assessment clients in online services update the permissions in the agent services account. The steps are in our guide to copying authorisations into the agent services account.
Which identifiers are used for PAYE and CIS?
HMRC’s PAYE for Agents service, which also covers CIS and Employment Related Securities, requires an agent reference number, the PAYE for Agents service enrolled on the HMRC online services account, and an authorisation for each client. On the paper 64 8, the PAYE and CIS sections ask for the client’s PAYE reference or CIS reference together with the agent Government Gateway identifier and the PAYE agent ID code, both described as needed for online access.
The agent Government Gateway identifier is found by signing in to HMRC online services for agents, selecting Authorise client and reading the entry headed Agent Identifier. A client who authorises the firm through their own business tax account needs this identifier. The full process is in getting authorised as agent for PAYE and CIS.
What about VAT and the smaller services?
Making Tax Digital for VAT uses the digital handshake through the agent services account. For the older VAT services in online services, an agent that is already VAT registered can use its own VAT number as its agent reference to enrol, while an unregistered agent applies online for an agent reference number for VAT. HMRC links VAT, VAT MOSS, NOVA and VAT EU Refunds for agents, so enrolling one adds the others and removing one removes all four.
Other services have their own references. HMRC lists an agent reference number or customer account reference number for charities, issued within 40 working days of receiving the application, and an agent reference number for Machine Games Duty, issued instantly. Gambling Tax needs no agent code at all.
How is a code turned into access?
In HMRC online services, a code on its own does nothing. The firm signs in, selects Services you can add, chooses Enrol for service and enters the agent code and postcode. HMRC then posts an activation code, which can take up to 7 days, and the service is only usable once the firm returns to the same screen and activates it. After that, each client still has to authorise the firm.
Which numbers belong to the client rather than the agent?
Staff often confuse the firm’s codes with the client’s references. The client’s Unique Taxpayer Reference, National Insurance number, company registration number, VAT registration number, CIS reference and employer PAYE reference identify the taxpayer, and the 64 8 asks for them in the section for each tax. The Client reference box on the agent side of the 64 8 is simply the firm’s own internal reference for that client.
| Identifier | System | Typical use |
|---|---|---|
| Agent reference number | Agent services account | Digital handshake services, repayment nominations |
| Self Assessment agent code | HMRC online services | Self Assessment for Agents, 64 8, copying authorisations for MTD |
| Corporation Tax agent code | HMRC online services | Corporation Tax for Agents, 64 8 |
| PAYE agent ID code and agent Government Gateway identifier | HMRC online services | PAYE and CIS authorisations |
How might this look for a real firm?
Illustration only. A two partner firm formed by merging two sole practices holds two Self Assessment agent codes, one Corporation Tax agent code and a PAYE for Agents enrolment. When it prepares for Making Tax Digital for Income Tax it adds only the code it uses day to day, and half its landlord clients are missing from the agent services account. Adding the second code brings them across. The firm also updates its repayment nomination template to use its ARN and the exact name held on the agent services account.
What mistakes come up most often?
- Writing a PAYE agent ID code or an ARN in the Agent code (SA) box of the 64 8.
- Trying to send a digital handshake while signed in with the online services user ID.
- Assuming every Self Assessment authorisation is in the agent services account when only one of several codes has been added.
- Enrolling a service and never activating it when the postal code arrives.
- Giving clients the wrong identifier for authorising through their business tax account.
Solar Protect runs fee protection schemes for accountancy and bookkeeping practices. See how our accountant schemes work or read fee protection schemes for accountants.
Related Accountapedia entries
- Signing up clients for MTD Income Tax
- Authorising an agent for trusts and estates
- How a client removes their agent
- Form 64 8: when it is still used
- Viewing client income records as an agent
Sources
- GOV.UK: Find out how to register as a professional tax agent with hmrc
- GOV.UK: Sign up your client for making tax digital for income tax
- GOV.UK: Check if and when you need to register as a tax adviser with hmrc
- GOV.UK: Receive income tax or paye repayments on behalf of others
- GOV.UK: How to use the digital handshake to get authorised as a tax agent
- GOV.UK: Authorising an agent to deal with your tax affairs
- GOV.UK: Self assessment for agents online service
- GOV.UK: Add your client authorisations for making tax digital for income tax
- GOV.UK: Payecis for agents online service
- GOV.UK: How to get authorised to act as a tax agent on behalf of your clients
Reviewed by Christine Anderson, Broker, Solar Protect. Last reviewed 19 October 2026. Part of Accountapedia, the Solar Protect guide to UK tax and accounting. This page is general information, not personalised advice.