If you're an accountant or tax agent in the UK, the 64-8 form is one of the most important documents in your practice. It's the legal instrument that authorises you to act on behalf of a client with HMRC — and yet, most practices still handle it on paper, by post, weeks before they can do any actual work.
That's changing. Here's everything you need to know about digital 64-8 forms in 2026, what HMRC's Making Tax Digital rollout means for agent authorisation, and how to get ahead of the shift before it becomes mandatory.
What Is a 64-8 Form?
The HMRC 64-8 is the standard form for "Authorising your agent." When a client signs a 64-8, they're formally authorising you — their accountant, tax adviser, or agent — to deal with HMRC on their behalf. This covers Self Assessment, PAYE, Corporation Tax, VAT, Construction Industry Scheme (CIS), and PAYE Settlement Agreements.
Without a signed 64-8 on file, HMRC will not discuss a client's tax affairs with you, even if the client is sitting next to you on the phone.
The Problem With Paper 64-8s
The traditional process: print the form, post it to the client, wait for them to sign it, wait for them to post it back, post it to HMRC, wait four to six weeks for HMRC to process it. Then — and only then — can you access the client's account on the Government Gateway.
For new client onboarding, this creates a bottleneck that can delay the start of real work by six weeks or more. It also creates compliance risk. Unsigned 64-8s, lost in the post or sitting unsigned on a client's desk, mean you're acting without formal authority — which creates professional indemnity exposure.
Digital 64-8s: What's Available Now
HMRC Online Services (Agent Services Account) You can invite clients to authorise you digitally through your Agent Services Account. The client receives an email, logs into their Government Gateway, and authorises you online. No paper, no post. Processing is near-instant. The limitation: the client must have an active Government Gateway account and be comfortable using it.
Digitally Signed 64-8 PDF HMRC currently accepts digitally signed 64-8 forms submitted via post as a transition measure. A platform like SignFlow Now allows you to send the 64-8 as a digitally signed document, get the client's e-signature in minutes, and maintain a cryptographic Certificate of Completion as your evidence of authorisation.
The MTD Timeline and What It Means for 64-8s
Making Tax Digital for Income Tax Self Assessment rollout:
- April 2026: Mandatory for sole traders and landlords with income over £50,000
- April 2027: Extends to those with income over £30,000
- April 2028: Extends to those with income over £20,000
Under MTD for ITSA, clients must use compatible software to keep digital records and submit quarterly updates. As their agent, you need formal authorisation in place before any of this begins. If you have clients coming into scope in April 2026 and haven't modernised your authorisation process, you're already behind.
What HMRC Requires for a Valid Digital Signature on a 64-8
For a digitally signed 64-8 to be valid, HMRC requires: identity verification, intent to sign, an audit trail, and tamper evidence. A qualified electronic signature meets all of these. SignFlow Now's Certificate of Completion provides a SHA-256 cryptographic hash, a complete audit trail including IP address, timestamp, and device information, and identity verification via government-issued ID.
Practical Steps for Digitising Your 64-8 Process
- Update your engagement letter template to reference the 64-8 authorisation
- Use a compliant e-signature platform that meets eIDAS standards and provides identity verification
- Send the 64-8 alongside your engagement letter in the same signing workflow
- Store the signed document and Certificate of Completion in your document management system
- Register the authorisation on HMRC's systems through your Agent Services Account
Common Questions
Can I use any e-signature platform for a 64-8? HMRC doesn't maintain a list of approved platforms. What matters is that the signature meets the legal requirements under the Electronic Communications Act 2000 and that you can provide evidence of authenticity if challenged.
Does the client need to print anything? No. A fully digital workflow means the client receives a link by email, views the document in their browser, signs electronically, and receives a copy automatically.
Does digital authorisation cover all taxes? Digital authorisation through HMRC's Agent Services Account covers MTD services. For older tax regimes, you may still need a paper 64-8 for some clients.
The Bottom Line
The 64-8 isn't glamorous, but it's the foundation of every client relationship you have with HMRC. With MTD for ITSA expanding scope through 2026 and 2027, now is the time to modernise. Digital 64-8s aren't just a convenience — they're increasingly the only way to keep pace with the volume of new authorisations your practice will need to process.
SignFlow Now's HMRC integration is currently in sandbox testing, with production credentials under review. Join the waitlist to be notified when direct HMRC submission goes live.