C · Client onboarding & engagement
How to Get HMRC Agent Authorisation for a New Client
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Quick answer
HMRC agent authorisation lets you act for a client on Self Assessment, Corporation Tax, VAT and PAYE through your Agent Services Account. You typically request authorisation digitally and the client approves it, or in some cases you use a paper form 64-8. Processing usually takes a few days once the client responds.
Key takeaways
- You need a separate authorisation for each tax you act on: SA, CT, VAT and PAYE are not linked automatically.
- Digital authorisation through your Agent Services Account is faster than paper 64-8 forms in most cases.
- Common rejection reasons include mismatched details, expired links and the client not completing their step.
- MTD for Income Tax authorisation follows the same ASA route but needs the client signed up separately.
- Keep a record of authorisation requests and dates as part of your onboarding checklist.
What's the difference between the Agent Services Account and the old Government Gateway agent system?
The Agent Services Account (ASA) is HMRC's newer platform, required for MTD services and increasingly for other taxes, while older Government Gateway agent credentials are being phased into it over time.
If you are starting a practice now, set up your ASA first — you will need it for MTD for Income Tax and it is the direction HMRC's systems are moving. You may still need your older agent Government Gateway ID for some legacy services in the transition period, so keep both live until HMRC confirms otherwise for your specific services.
How long does HMRC agent authorisation take?
Digital authorisation can complete within a few days of the client approving the request, while paper 64-8 forms can take several weeks to process.
The main variable is not HMRC's processing speed but how quickly your client acts on the link or letter you send them. Build a follow-up step into onboarding so authorisation requests don't sit unopened in a client's inbox for weeks, especially where a filing deadline is approaching.
How to get HMRC agent authorisation for a new client
- 1
Set up your Agent Services Account
Register your firm for an ASA if you have not already, linking it to your AML supervision details.
- 2
Confirm which taxes you need authorisation for
Check whether the client needs SA, CT, VAT, PAYE or MTD ITSA authorisation, or a combination.
- 3
Generate the authorisation request
Use your ASA or software to create a digital link, or complete form 64-8 where digital authorisation is not available.
- 4
Send the request to the client
Share the link or form with clear instructions and a deadline for them to act.
- 5
Follow up if unactioned
Chase after a week if the client hasn't approved the request, especially near a filing deadline.
- 6
Confirm authorisation is active
Check your agent dashboard or client list to confirm the client now shows as authorised.
- 7
Record the authorisation date
Note the date and tax type in your onboarding file for future reference.
How Remindoo helps
Getting agent authorisation sorted early is one of the standard onboarding tasks Remindoo helps you track, alongside identity checks and the engagement letter, as part of a repeatable onboarding request for every new client. You can set a task with a follow-up reminder so an unactioned authorisation link doesn't get forgotten while you're focused on other new clients. Once authorisation is confirmed, automated reminders and trigger dates keep upcoming deadlines for that client visible, which matters particularly when a first filing is due soon after the client joins. It turns a step that's easy to overlook into a checked, dated item on the client's record.
Frequently asked questions
Why was my agent authorisation request rejected?
Common reasons include mismatched client details, an expired authorisation link, the wrong reference number used, or the client not completing their approval step.
Do I need a new authorisation if the client changes accountant again later?
Yes, authorisation is specific to your firm; a new accountant would need to request their own authorisation and the previous agent's access would typically be removed.
Can I be authorised for VAT without being authorised for Self Assessment?
Yes, each tax requires separate authorisation, so you can hold VAT authorisation only if that's the sole service you provide.
Does authorisation cover MTD for Income Tax automatically?
No, the client also needs to be signed up to MTD ITSA separately before quarterly update authorisation becomes fully active.
What if the client has never used HMRC online services before?
They will need to set up a Government Gateway account before they can approve a digital authorisation request.
Is form 64-8 still valid?
Yes for some services, though HMRC is steadily moving more processes to digital authorisation via the Agent Services Account.
How do I check which clients I'm currently authorised for?
Your agent services dashboard or practice software integration should list active client authorisations by tax type.
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Sources
Last updated 23 September 2026. General guidance, not legal or regulatory advice. Check with your professional body.
