Form 64-8 Formal Authorisation to Act as a Tax Agent: An In-Depth Overview

Form 64-8 is the formal authorisation document that allows tax agents to deal directly with HMRC on behalf of their clients. Without this, even the most experienced accountant cannot access a client’s tax records, correspond with HMRC, or manage their affairs.

This comprehensive guide explains what Form 64-8 is, the types of tax matters it covers, and the correct process for completing and submitting it to HMRC.

What Is Form 64-8?

Form 64-8 is a formal document that authorises an accountant or tax agent to act on behalf of a client in dealings with HMRC. It establishes a legal relationship between the taxpayer and the agent, giving the agent permission to access certain tax records, make enquiries, and correspond with HMRC.

The form is completed and signed by the taxpayer (or an authorised signatory in the case of a company), and then submitted to HMRC by the agent.

HMRC uses this form to confirm that the client has given explicit consent for the agent to act on their behalf. Without it, HMRC will not deal with the agent regarding that client’s affairs.

Form 64-8 and Mandatory Tax Adviser Registration (MMTAR)

Since 18 May 2026, the Modernising and Mandating Tax Adviser Registration (MMTAR) regime has required anyone paid to interact with HMRC on behalf of clients to register through an Agent Services Account (ASA). Registration is being phased in across four windows running to 31 March 2027, depending on the adviser's existing HMRC registration status. This is a separate requirement from Form 64-8, and one does not replace the other.

MMTAR registers the firm or individual as a recognised tax adviser with HMRC. Form 64-8 authorises that adviser to act for one specific client on specific tax matters. A firm that has completed MMTAR registration still needs a valid 64-8, or online authorisation through the ASA, for each individual client relationship.

If your firm already holds an Agent Services Account, HMRC has confirmed you do not need to register again under MMTAR. You will be moved to the new digital service and contacted directly if further information is required. If you interact with HMRC on behalf of clients but do not yet have an ASA, check which MMTAR registration window applies to your firm before relying on an existing 64-8 or paper-based authorisation alone.

What Tax Matters Does Form 64-8 Cover?

Form 64-8 can authorise an agent to act on a client’s behalf for a range of tax matters, including:

• Self Assessment (individuals and partnerships)
• PAYE for employers
• Corporation Tax
• VAT
• Tax Credits
• National Insurance Contributions
• CIS (Construction Industry Scheme)

The form allows the client to specify which tax matters the agent is authorised to deal with. A single form can cover multiple tax types.

How to Complete Form 64-8

Section 1: Client Details

This section requires the taxpayer’s full name, address, date of birth (for individuals), and relevant tax reference numbers (UTR, NINO, employer PAYE reference, VAT registration number, etc.).

Section 2: Agent Details

The agent’s full name, firm name, address, telephone number, and HMRC agent code must be provided. HMRC uses the agent code to identify the firm within its systems.

Section 3: Tax Matters

This section specifies which taxes the agent is authorised to deal with. The client ticks the relevant boxes and provides the corresponding reference numbers.

Section 4: Declaration

The client (or an authorised signatory) signs and dates the form. For companies, the signatory must be a director or company secretary. HMRC will not accept forms signed by the agent on behalf of the client.

How to Submit Form 64-8 to HMRC

The completed form should be sent to the relevant HMRC office, depending on the tax type. For Self Assessment, it goes to the SA section. For VAT, it goes to the VAT registration office. For PAYE, it is sent to the employer’s HMRC office.

Agents can also set up authorisation online through HMRC’s agent services account for certain tax types. Online authorisation is typically processed faster than paper submissions.

Online Agent Authorisation

For Self Assessment, agents can request authorisation online through the agent services account. HMRC sends a code to the client by post, and the client provides this code to the agent to complete the process.

Online authorisation is generally approved within 24 to 72 hours, compared to several weeks for paper submissions.

Common Mistakes When Completing Form 64-8

The most frequent errors include:

• Missing or incorrect tax reference numbers
• Form not signed by the client (or signed by the agent instead)
• Incorrect agent code
• Not specifying which tax matters the authorisation covers
• Sending the form to the wrong HMRC office

Any of these errors will result in the form being rejected, causing delays in setting up the agent relationship.

Revoking Agent Authorisation

Either the client or the agent can revoke the authorisation at any time. The client can do so by writing to HMRC directly. The agent can remove the authorisation through their agent services account online.

If a client changes accountants, the new agent’s authorisation automatically replaces the previous one for the same tax type. There is no need to formally revoke the old authorisation first.

Security and Confidentiality

Form 64-8 contains sensitive personal and tax information. Agents must handle the form in accordance with GDPR requirements and their professional body’s confidentiality rules.

Paper forms should be stored securely. Where digital copies are retained, they must be protected by appropriate encryption and access controls.

Form 64-8 for Companies

When acting for a company, the form must be signed by a director or company secretary. The company’s UTR and, where applicable, employer PAYE reference and VAT registration number must be provided.

For Corporation Tax authorisation, agents should also be aware that HMRC may require additional verification before granting access.

Best Practices for Managing 64-8 Authorisations

Firms should maintain a register of all client authorisations, including the date the form was submitted, the tax types covered, and confirmation of acceptance by HMRC.

Regular reviews should check that authorisations remain current and that no gaps exist where clients have been taken on without a valid 64-8 in place.

Using practice management software with built-in 64-8 tracking helps ensure nothing falls through the gaps.

FigsFlow and Agent Authorisation

FigsFlow integrates the 64-8 process into your client onboarding workflow. When a new client accepts their engagement letter, FigsFlow automatically generates the 64-8 for the relevant tax types and collects the client’s electronic signature.

This eliminates the manual steps of printing, posting, and chasing forms, reducing the time between engagement and active representation.

Additional Resources

• HMRC Agent Registration Guide for Tax Advisers
• Download Form 64-8 from GOV.UK

Frequently Asked Questions